WebUI connection timeout after IP change

I know this has been asked before, but the answers I found didn't help out.

This problem occurs on a proxmox (v2) installation with only one host (i.e. no cluster).

After changing the IP in "/etc/network/interfaces" and "/etc/hosts" PING and SSH works, but I can't connect to the WebUI via https://<NewIP>:8006.

Things I've tried:
- reboot of the machine
- creation of a interfaces.new file + reboot
- setting the host parameter in "/usr/bin/pveproxy"

Are there any other files I should check for the old IP? How can I tell the WebServer (pveproxy?) to use the new IP?

Regards