Are you hosting your CMS instances on Windows Server or Docker?
I discovered that, when running Xibo on Windows Server, the cache library path can sometimes become too long. Since Windows has a path length limit, Xibo/PHP may fail to read cached files if the full path exceeds that limit. This could potentially be causing the issue you are experiencing.
I’m not sure whether the same issue can also happen on a non-Docker Debian installation, but it may be worth investigating whether PHP is able to properly handle and read the cache files inside your library folder.