Whiteboard does not load file for one user

As described, out of four users who tried, for one specific user Whiteboards do no longer load. The window screen goes white (or black in dark mode) but neither content nor menus show up nor does any error message. It worked originally without problem and suddenly and without any relatable occurrence stopped working. All whiteboard files are affected. The files also do not open after a long loading time.

There are no errors in the logs on warning log level that I can bring into relation to Whiteboard at all.

The user is using an up to date Firefox without addons and completely unmodified settings on Windows. The user can open whiteboards on another device from that account.

Whiteboard is installed as part of the Nextcloud AIO 12.1.4 along with Nextcloud 32.0.2 and using the predefined docker container running on Linux without reverse proxy, cloudflare or such things. There have been no changes to Whiteboard in any way. Whiteboard was first installed on this server in April this year, if I remember correctly. integration_whiteboard has not been installed before.

Is there anything that can be done or should be checked to provide more info?

No files or tests are identified. Start by reproducing the Whiteboard loading failure for the affected user in Firefox on Windows and compare it with another device or account; done means identifying a reproducible cause or collecting actionable browser or server errors.