I had the same problem.
Since I connected several additional interfaces, I've always had these freezes.
Previously there was only one (server network), now I had to add three more because I set up my backup firewall as a VM.
I had assigned each interface its IP, which it should have within the VM. From then on, the freezes.
Now I've removed the CIDRs (left them empty) - the firewall is still working fine (the IPs are configured internally) and I've had a terminal window open for half an hour and nothing has frozen!
The only assigned IP (including subnet) is the server network, in which Proxmox itself is located.
So: 4 adapters, 4 bridges; only 1 IP assigned for a bridge, which I use (via browser) to connect to the poor VMs that don't (yet) have a network.