[Bug]: Stuck "Couldn't convert to placeholder" sync error, even if file got synced properly

### ⚠️ 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

The desktop client constantly reports that a file could not be synced. While syncing, I can briefly see there error "Couldn't convert to placeholder". The message disappears once the sync is finished.

This is not the first time the bug has happened. I managed to work around it by renaming the file to something else and then back to its original name. It did not work this time around...

It's worth noting that the file gets properly synced. It's just a very annoying error message. I can see the file on nextcloud web, download it and read it fine.

There are multiple reports of this problem on github, all closed.

### Steps to reproduce

Happens quite randomly, I have no idea how to reproduce the issue.
What I can say is that I'm using virtual file sync and that the file is in a nextcloud group folder.

### Expected behavior

Syncing is marked has finished.
Also, it would be nice if the error stayed displayed and above all other messages so that it is easier to understand that there is a problem.

### Which files are affected by this bug

A wav file, but it already happened multiple times with different types of files (images, videos...)

### Operating system

Windows

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

Windows 11

### Package

Official Windows MSI

### Nextcloud Server version

32.0.1

### Nextcloud Desktop Client version

4.0.1

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

Updated from a minor version (ex. 3.16.1 to 3.16.2)

### 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
Nothing much happens server side, just a bunch of PROPFIND. Logical since there is nothing to sync.
```

### Additional info

[20251120_1136_nextcloud.log](https://github.com/user-attachments/files/23651942/20251120_1136_nextcloud.log)