There is a file
web-lib-funcs.pl (in your case I think located in
/usr/share/webmin/..). Make sure that it's same as on the Webmin repo and has
sub list_combined_system_info string or
Afterwards make sure to clear Webmin's cache. You can do it different ways. Easiest way to go to
Webmin->Webmin Configuration->Webmin Scheduled Functions, tick those checkboxes (
scheduled_collect_system_info) and click
Run Selected Functions Now.
Don't forget to restart Webmin after all using CLI.
I don't know how did you install Webmin but having
webmin-1.760 on its path could be the possible cause.
The other possible cause is that your Perl pointer, like '#!/usr/bin/perl' is wrong in case of manual installation.
Reboot the system if nothing works.
I think it's just the cache issue. In case you use Chrome it's very possible. Open DevTools (F12) and then hold refresh button to make hard reset. After close and reopen your browser. Try other browsers, like Firefox.