Based on forum post: https://www.virtualmin.com/comment/757228 (I hope I'm right I have to create this issue in order to request your premium support, I bought a "issue" but don't know how to activate it)
Debian 6 (Squeeze) Version 5.03 Webmin 1.801
Everything should be up-to-date.
I can't login the controlpanel (https://domain.tld:10000). - With authentic theme: the bar at the side loads, but the main frame keeps grey and 'loading' - With the default theme (when I remove authentic theme from the /etc/webmin/config) it keeps on loading and after a long time, I get error "Failed to lock file /etc/group after 5 minutes. Last error was :"
I found many lockfiles (like /etc/passwd.lock) and they keep on appearing when I delete them.
Some processes, like: - /usr/share/webmin/authentic-theme/index.cgi - something.../domain-list.pl - /usr/share/webmin/virtual-server/collectinfo.pl
Keep on running at 100% CPU and using much memory (like 10GB).
Everything worked well (also after reboots etc.) before I installed 5.03.