Pardon intrusion to discussion ...
2 Questions:
1. does server have a valid cert? Not self generated or generated by #2 ...
2. does the network upon which it resides have anything in front of the moodle ... like something that would "guard' the moodle server?
What would happen if, from the command line of your server, using elinks (text based browser) to the server url by FQDN and via http and then again with https
'spirit of sharing', Ken