From what I understand Authentic Theme is not to be updated as stand alone.
If you have Virtualmin installed from the Virtualmin installer? You are only to update Webmin/Usermin and Authentic Theme when you receive the message in Package Updates to do so.
Other wise you can break your Virtualmin installation.
Virtualmin version 7.20.2 should have versions
Webmin 2.111
Usermin 2.010
Authentic Theme 21.10
Webmin Standalone install
Webmin 2.201
Authentic Theme 21.20.3
Both these installations on my end show no issue with “memory leak”