Unable to add user to Guests group

Steps to reproduce

Go to /settings/users/guest_app
Create a new guest account using the default settings (Group: Guests, “Member of the following group: Guest”)
After creation, refresh /settings/users/guest_app

Expected behaviour

The newly created account remains visible in the Guests view and is a member of the Guests group.

Actual behaviour

After refreshing the page:
The account disappears from the Guests view
The account still exists under All Accounts
The user cannot be re-added to the Guests group via the dropdown (UI unresponsive)

Verification

User account exists and is active
User is visible in All Accounts
Guest group membership is not reflected in the Guests view after refresh

Server configuration

Web server: Apache (Nextcloud AIO nextcloud-aio-apache), behind Caddy reverse proxy
Operating system: Ubuntu 24.04.3 LTS (host)
Database: PostgreSQL
PHP version: 8.3
Nextcloud version: Nextcloud Hub 25 (32.0.4)
Guests app version: 4.6.0
Docker version: 29.1.3

Browser
Browser: Firefox
Version: 147

Logs

Reproduced issue while tailing Nextcloud logs via:
docker exec -u www-data nextcloud-aio-nextcloud php occ log:tail -f --raw
No guest-related errors or exceptions were logged at the time of failure.

Firefox console shows CSP warnings only (no CSP violations or blocked scripts).

Start by reproducing the issue at /settings/users/guest_app with the default Guests group settings, then inspect the guest membership handling across the app's JavaScript and PHP entry points. Use the provided occ log:tail command while refreshing the page. Done means the account remains in the Guests view after refresh and can be assigned to the Guests group through the dropdown.