New devices connecting via webui are shown the setup wizard instead of login page.

[lxl]

I just noticed you didn't explicitly define a /cache directory.  Where does that end up going?  Because the cache clean up job runs periodically and I wonder if those clean up runs correspond to your issue.  If the config directory is placed within /cache in the VFS it may be getting wiped periodically.  Try explicitly defining /cache and putting it in a distinct folder on the host file system.

Jellyfin seem to place cache in $config/jellyfin/cache