Also reported on the German language forum as well: https://forum.proxmox.com/threads/proxmox-pve-proxy-h%C3%A4ngt-sich-immer-auf.164744/post-762074. Seems patches are already made ;-)
Error log flooded with:
detected empty handle
Can't use an undefined value as a symbol reference at /usr/share/perl5/PVE/APIServer/AnyEvent.pm line 150
After this starts pvemanager is not accessible anymore.
I have tried this: apt reinstall...