Connection error - server offline

[cola16]

I bought a new network interface card and set up the existing network as bonding.
After that, I get a "Connection error - server offline?" error when doing certain tasks in proxmox web.

There is no problem restarting the host but when I connect to the shell, I get Connection failed (Error 501.
I can see the console of the vm or change the settings of the vm,
but when I press shutdown or start the vm I get "Connection error - server offline?"

ping between VMs or between PVE hosts works.
ip does not changed.
Changed from bridge20-enp7s0 to bridge20-bond20-enp7s0.

 

[cola16]

I misanalyzed the cause

Yesterday, I add new network bonding. also I update proxmox machines.

During the update process, cloudflare was updated, and it seems to be the cause of the problem
If I access it directly with the IP address, it works