Hi there, Rick. Still working through it all. I think it's related to the database upgrade or conversion right now. Will keep the thread updated!
For others monitoring or advising ...
Moodle upgraded successfully via command line ... now using git.
But access kept throwing a false error 500 to clients.
Apache logs showed access denied ... and other errors in 400's.
Caught by Erin himself ... good sluething considering ...
suPHP SoftException error ... group ownerships of directories and files ... a no no by suPHP 'standards' ....
For others that might find themselves in similar ...
https://www.suphp.org/Home.html
suPHP is not maintained any longer and will not receive any further updates not even security patches. If you want to continue using suPHP, feel free to create a fork (the complete code is licensed under the GPL version 2).
If you are looking for an alternative, have a look at php-fpm.
There also is a fork of suPHP maintained by John Lightsey on GitHub.
Is server using the fork or the old (non-supported) suPHP? Since server actually has mod_security running, maybe suPHP no longer needed.
Progress being made ... but much more to do ...
When a private channel of communications is opened, sometimes the issue with Moodle is related to overall hosting ... and what ... and how many ... etc.
Set up is a reseller account/server (normally meant to be the 'controller' for other servers allocated from said server) with 8 Gig memory (a power house 10+ years ago) for 10+ WPressees + vBulletin forum by different domains ... thus also running Bind DNS - all hosted on this one server.
While server has easy apache and PHP versions can be set per directory via .htaccess files, DB requirements for 3.7 might/would affect WP's (all below 5.x) and VBulletin. One DB server ... on same box as WHM, cPanel, etc.
Server now using a big chunk of SWAP space ... until OP can inquire with hosting provider about a memory upgrade or what options there are for keeping reseller box and getting more memory.
'SoS', Ken