[Bug]: Nextcloud Desktop client 33.0.2 crash during Server upgrade

### ⚠️ Before submitting, please verify the following: ⚠️

- [x] This is a **bug**, not a question or a configuration issue.
- [x] This issue is **not** already reported on Github (I've searched it).
- [x] Nextcloud Server and Desktop Client are **up to date**. See [Server Maintenance and Release Schedule](https://github.com/nextcloud/server/wiki/Maintenance-and-Release-Schedule) and [Desktop Releases](https://nextcloud.com/install/#install-clients) for supported versions.
- [x] I agree to follow Nextcloud's [Code of Conduct](https://nextcloud.com/contribute/code-of-conduct/)

### Bug description

Nextcloud Desktop client (AppImage 33.0.2 on Fedora 43) crashes during a succesfull server upgrade from 33.0.0 to 33.0.2.
...

### Steps to reproduce

1. Connect Nextcloud desktop client to an existing Nextcloud server version 33.0.0
2. Start the upgrader process on the serer
3. During upgrade the client crashes
...

### Expected behavior

Client loses connection during maintenacne but startes syncing as soon as maintenance is stopped
...

### Which files are affected by this bug

none

### Operating system

Linux

### Which version of the operating system you are running.

Fedora 43 6.19 KDE Plasma 6.6.3

### Package

Official Linux AppImage

### Nextcloud Server version

33.0.0 -> 33.0.2

### Nextcloud Desktop Client version

33.0.2

### Is this bug present after an update or on a fresh install?

Fresh desktop client install

### Are you using the Nextcloud Server Encryption module?

Encryption is Disabled

### Are you using an external user-backend?

- [x] Default internal user-backend
- [ ] LDAP/ Active Directory
- [ ] SSO - SAML
- [ ] Other

### Nextcloud Server logs

```shell
After the update the logs are empty
```

### Additional info

Crashed process viewer:

```
PID: 47481 (AppRun)
UID: 1000 (j)
GID: 1000 (j)
Signal: 11 (SEGV)
Timestamp: Wed 2026-04-08 09:28:50 CEST (16s ago)
Command Line: Applications/Nextcloud-33.0.2-x86_64.AppImage
Executable: /tmp/.mount_NextclnmjBdm/usr/bin/nextcloud
Control Group: /user.slice/user-1000.slice/user@1000.service/app.slice/app-org.kde.konsole-6904.scope/tab(12676).scope
Unit: user@1000.service
User Unit: app-org.kde.konsole-6904.scope
Slice: user-1000.slice
Owner UID: 1000 (j)
Boot ID: 734fa5640ef9470d903f957617be036e
Machine ID: 97b658c4dc2d411eabf1b2a547c49718
Hostname: ws-study
Storage: /var/lib/systemd/coredump/core.AppRun.1000.734fa5640ef9470d903f957617be036e.47481.1775633330000000.zst (present)
Size on Disk: 30.2M
Message: Process 47481 (AppRun) of user 1000 dumped core.

Module /tmp/.mount_NextclnmjBdm/usr/lib/libxcb-glx.so.0 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libxcb-glx.so.0
Module /tmp/.mount_NextclnmjBdm/usr/lib/libxcb-xkb.so.1 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libxcb-xkb.so.1
Module /tmp/.mount_NextclnmjBdm/usr/lib/libxcb-shape.so.0 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libxcb-shape.so.0
Module /tmp/.mount_NextclnmjBdm/usr/lib/libxcb-render.so.0 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libxcb-render.so.0
Module /tmp/.mount_NextclnmjBdm/usr/lib/libxcb-xfixes.so.0 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libxcb-xfixes.so.0
Module /tmp/.mount_NextclnmjBdm/usr/lib/libxcb-sync.so.1 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libxcb-sync.so.1
Module /tmp/.mount_NextclnmjBdm/usr/lib/libxcb-shm.so.0 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libxcb-shm.so.0
Module /tmp/.mount_NextclnmjBdm/usr/lib/libxcb-render-util.so.0 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libxcb-render-util.so.0
Module /tmp/.mount_NextclnmjBdm/usr/lib/libxcb-randr.so.0 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libxcb-randr.so.0
Module /tmp/.mount_NextclnmjBdm/usr/lib/libxcb-keysyms.so.1 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libxcb-keysyms.so.1
Module /tmp/.mount_NextclnmjBdm/usr/lib/libxcb-image.so.0 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libxcb-image.so.0
Module /tmp/.mount_NextclnmjBdm/usr/lib/libxcb-util.so.1 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libxcb-util.so.1
Module /tmp/.mount_NextclnmjBdm/usr/lib/libxcb-icccm.so.4 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libxcb-icccm.so.4
Module /tmp/.mount_NextclnmjBdm/usr/lib/libxkbcommon-x11.so.0 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libxkbcommon-x11.so.0
Module /tmp/.mount_NextclnmjBdm/usr/lib/libblkid.so.1 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libblkid.so.1
Module /tmp/.mount_NextclnmjBdm/usr/lib/libcap.so.2 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libcap.so.2
Module /tmp/.mount_NextclnmjBdm/usr/lib/liblz4.so.1 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/liblz4.so.1
Module /tmp/.mount_NextclnmjBdm/usr/lib/libgomp.so.1 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libgomp.so.1
Module /tmp/.mount_NextclnmjBdm/usr/lib/libcrypto.so.1.1 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libcrypto.so.1.1
Module /tmp/.mount_NextclnmjBdm/usr/lib/libkeyutils.so.1 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libkeyutils.so.1
Module /tmp/.mount_NextclnmjBdm/usr/lib/libkrb5support.so.0 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libkrb5support.so.0
Module /tmp/.mount_NextclnmjBdm/usr/lib/libk5crypto.so.3 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libk5crypto.so.3
Module /tmp/.mount_NextclnmjBdm/usr/lib/libkrb5.so.3 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libkrb5.so.3
Module /tmp/.mount_NextclnmjBdm/usr/lib/libselinux.so.1 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libselinux.so.1
Module /tmp/.mount_NextclnmjBdm/usr/lib/libmount.so.1 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libmount.so.1
Module /tmp/.mount_NextclnmjBdm/usr/lib/libsystemd.so.0 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libsystemd.so.0
Module /tmp/.mount_NextclnmjBdm/usr/lib/libgssapi_krb5.so.2 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libgssapi_krb5.so.2
Module /tmp/.mount_NextclnmjBdm/usr/lib/libGLdispatch.so.0 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libGLdispatch.so.0
Module /tmp/.mount_NextclnmjBdm/usr/lib/libEGL.so.1 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libEGL.so.1
Module /tmp/.mount_NextclnmjBdm/usr/lib/libxkbfile.so.1 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libxkbfile.so.1
Module /tmp/.mount_NextclnmjBdm/usr/lib/libxshmfence.so.1 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libudev.so.1 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libudev.so.1
Module /tmp/.mount_NextclnmjBdm/usr/lib/libXi.so.6 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libXi.so.6
Module /tmp/.mount_NextclnmjBdm/usr/lib/libXtst.so.6 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libXtst.so.6
Module /tmp/.mount_NextclnmjBdm/usr/lib/libXrender.so.1 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libXrender.so.1
Module /tmp/.mount_NextclnmjBdm/usr/lib/libXrandr.so.2 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libXrandr.so.2
Module /tmp/.mount_NextclnmjBdm/usr/lib/libXfixes.so.3 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libXfixes.so.3
Module /tmp/.mount_NextclnmjBdm/usr/lib/libXext.so.6 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libXext.so.6
Module /tmp/.mount_NextclnmjBdm/usr/lib/libXdamage.so.1 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libXdamage.so.1
Module /tmp/.mount_NextclnmjBdm/usr/lib/libXcomposite.so.1 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libXcomposite.so.1
Module /tmp/.mount_NextclnmjBdm/usr/lib/libatomic.so.1 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libatomic.so.1
Module /tmp/.mount_NextclnmjBdm/usr/lib/libxkbcommon.so.0 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libxkbcommon.so.0
Module /tmp/.mount_NextclnmjBdm/usr/lib/libOpenGL.so.0 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libOpenGL.so.0
Module /tmp/.mount_NextclnmjBdm/usr/lib/libGLX.so.0 without build-id.
Module /tmp/.mount_NextclnmjBdm/usr/lib/libGLX.so.0
Module libnss_resolve.so.2 from rpm systemd-258.7-1.fc43.x86_64
Module libnss_mdns4_minimal.so.2 from rpm nss-mdns-0.15.1-27.fc43.x86_64
Module libnss_myhostname.so.2 from rpm systemd-258.7-1.fc43.x86_64
Module libGL.so.1 from rpm libglvnd-1.7.0-8.fc43.x86_64
Module libVkLayer_MESA_device_select.so from rpm mesa-25.3.6-3.fc43.x86_64
Module libvulkan_nouveau.so from rpm mesa-25.3.6-3.fc43.x86_64
Module libvulkan_lvp.so from rpm mesa-25.3.6-3.fc43.x86_64
Module libvulkan_dzn.so from rpm mesa-25.3.6-3.fc43.x86_64
Module libdisplay-info.so.2 from rpm libdisplay-info-0.2.0-4.fc43.x86_64
Module libwayland-client.so.0 from rpm wayland-1.24.0-1.fc43.x86_64
Module libvulkan.so.1 from rpm vulkan-loader-1.4.341.0-1.fc43.x86_64
Module libtinfo.so.6 from rpm ncurses-6.5-7.20250614.fc43.x86_64
Module libpciaccess.so.0 from rpm libpciaccess-0.16-16.fc43.x86_64
Module libedit.so.0 from rpm libedit-3.1-57.20251016cvs.fc43.x86_64
Module libdrm_intel.so.1 from rpm libdrm-2.4.131-1.fc43.x86_64
Module libelf.so.1 from rpm elfutils-0.194-1.fc43.x86_64
Module libdrm_amdgpu.so.1 from rpm libdrm-2.4.131-1.fc43.x86_64
Module libsensors.so.4 from rpm lm_sensors-3.6.0-23.fc43.x86_64
Module libSPIRV-Tools.so from rpm spirv-tools-2026.1-2.fc43.x86_64
Module libxcb-present.so.0 from rpm libxcb-1.17.0-6.fc43.x86_64
Module libXxf86vm.so.1 from rpm libXxf86vm-1.1.6-3.fc43.x86_64
Module libdrm.so.2 from rpm libdrm-2.4.131-1.fc43.x86_64
Module libgallium-25.3.6.so from rpm mesa-25.3.6-3.fc43.x86_64
Module libGLX_mesa.so.0 from rpm mesa-25.3.6-3.fc43.x86_64
Module libX11-xcb.so.1 from rpm libX11-1.8.13-1.fc43.x86_64
Module libcom_err.so.2 from rpm e2fsprogs-1.47.3-2.fc43.x86_64
Module libxml2.so.2 from rpm libxml2-2.12.10-5.fc43.x86_64
Module libXau.so.6 from rpm libXau-1.0.12-3.fc43.x86_64
Module libasound.so.2 from rpm alsa-lib-1.2.15.3-1.fc43.x86_64
Module libxcb.so.1 from rpm libxcb-1.17.0-6.fc43.x86_64
Module libfontconfig.so.1 from rpm fontconfig-2.17.0-3.fc43.x86_64
Module libX11.so.6 from rpm libX11-1.8.13-1.fc43.x86_64
Module libxcb-dri3.so.0 from rpm libxcb-1.17.0-6.fc43.x86_64
Stack trace of thread 47481:
#0 0x00007fd7ecc97a85 n/a (/tmp/.mount_NextclnmjBdm/usr/lib/libQt6Network.so.6 + 0x97a85)
#1 0x00007fd7ef78a044 n/a (/tmp/.mount_NextclnmjBdm/usr/lib/libnextcloudsync.so.0 + 0x58a044)
#2 0x00007fd7ef717bae n/a (/tmp/.mount_NextclnmjBdm/usr/lib/libnextcloudsync.so.0 + 0x517bae)
#3 0x00007fd7ef719ae2 n/a (/tmp/.mount_NextclnmjBdm/usr/lib/libnextcloudsync.so.0 + 0x519ae2)
#4 0x00007fd7ef717c20 n/a (/tmp/.mount_NextclnmjBdm/usr/lib/libnextcloudsync.so.0 + 0x517c20)
#5 0x00007fd7ef714b92 n/a (/tmp/.mount_NextclnmjBdm/usr/lib/libnextcloudsync.so.0 + 0x514b92)
#6 0x00007fd7ef70fb87 n/a (/tmp/.mount_NextclnmjBdm/usr/lib/libnextcloudsync.so.0 + 0x50fb87)
#7 0x00007fd7ec609222 n/a (/tmp/.mount_NextclnmjBdm/usr/lib/libQt6Core.so.6 + 0x209222)
#8 0x00007fd7ec5fabdf n/a (/tmp/.mount_NextclnmjBdm/usr/lib/libQt6Core.so.6 + 0x1fabdf)
#9 0x00007fd7ee392eea n/a (/tmp/.mount_NextclnmjBdm/usr/lib/libQt6Widgets.so.6 + 0x192eea)
ELF object binary architecture: AMD x86-64
```
Coredump: https://cloud.sbw.media/index.php/s/tKLYrAW9ZxdcgW2