Well there is my confusion with versions: In the GUI main page webmin it displays Virtualmin version 7.7 and i thought it should appear 7.7.2, but that gpl-2 can be seen after i run command that you mentioned earlier:
cat /usr/share/webmin/virtual-server/module.info | grep version=
I have the gpl-2. But the issue still continue with subservers backups. They still throw that error.
**
PE:
**
I solved issue with backups for subservers. Here i found at Cameron a lead to solve the issue: https://forum.virtualmin.com/t/backup-problem-after-upgrade-virtualmin/120371
I edited and modified files: /usr/share/webmin/virtual-server/lang/en (you find modified lines on github in the above link)
Also : /usr/share/webmin/virtual-server/feature-dns.pl (also on github)
I restarted webmin server after modifications and now backups are working.