CentOS 8 - 8.3.2011, Virtualmin version - 6.16 - Broken frontend, related to Themes

OS: CentOS 8 - 8.3.2011
Webmin version - 1.973
Usermin version - 1.823
Virtualmin version - 6.16

Hi!
First of all I love the development that goes into virtualmin/webmin, so far I have always managed to resolve all issues myself but this one has been bothering me for about a week now and I would like to be pointed into the right direction.
After accidentally stopping the Usermin service about a week ago, I started encountering weird UI / Theme glitches. I had immediately restarted the server to reload everything and load Usermin, but the issues never went away.
As a resolution, I have to force refresh the tab approx 3-6 times - after a few refreshes, it just decides to load with no issues (until my browsing session ends that is). My issues include:

I’ve tried changing Theme configuration to default but it made no difference, any help or troubleshooting steps are greatly appreciated.

Any ideas anyone? Feeling hopeless with this :face_with_head_bandage: