I was having the same problem, after editing the IP address from 192.168.1.8 to 192.168.1.10, I was getting an error where I couldn't login to the web interface, or I can get in but none of the GUI was working. I previously had another pve server with 192.168.1.10, and the new hardware was temporarily being setup as 192.168.1.8. Once I was ready, I shutdown the 192.168.1.10, and then changed the IP address of the new server to 192.168.1.10 and was having problems.
I did some "systemctl restart pvedaemon pveproxy" and also system reboot as suggested from the thread, but it didn't make much change. Trying a different browser, I found that my previous pve server certificate was stored in Chrome and that was interfering.
So in the end, I had to copy the new certificate from /etc/pve/nodes/{my-server-name}/pve-ssl.pem and import that as a custom certificate in Chrome (chrome://certificate-manager/).