this is all for the gpl code.
when trying to use usermin directly, or by using the 'login to usermin' button. i am usually getting a mostly blank screen (the left menu is usually there, but nonfunctional). but, sometimes i get an error:
Failed to save user : Invalid PID file
if i restart usermin, then sometimes the first user i connect as will work normally.
this is affecting centos 6 and 7 as well as ubuntu 14.04.
Webmin version 1.870 Usermin version 1.720 Virtualmin version 6.02 Theme version Authentic Theme 19.04
i see quite a few errors in miniserv.errors, but that is a pretty noisy place to begin with, so even in the case when it is working for one user, there are plenty of warnings showing up.