Cannot start backup

Dear all,
I am on HAOS 14.1, Core 2025.1.4 running as proxmox VM. I recently updated HA and configured automatic backup on local drive and router nas. Since then, updates do not work at all. The backup button is greyed out. The system is in freeze state.
If I restart the VM and get lucky I can manually create a backup once. The next day, its time for backing up again, but it again does not work. It says “Creating backup” all the time and the wheel is spinning.
I deactivated automatic backups and restarted, but no improvement.
Any suggestions?