We recently changed over from one server to a brand new one.
Old server: PHP 5.7, Joomla 2.x, MySQL 5.6.x
New Server: PHP 7.0, Joomla 3.x, MariaDB 10.x.
The OSE Plugin is the different, but given that it is affecting rows outside of OSE (They seem to be defunct now, as we are not getting any reply from their support staff).
On both servers, this glitch can be replicated, but not 100% of the time.
Near as we can tell, any value that is entered into the table that contains "select", "selected", or any other variation of the word results in a generic 500 error. This happens when changing an article that includes the word, when changing an email template in the OSE control panel (e.g. "membership selected:"), or when trying to change those rows manually through a PHPMyAdmin installed manually.
Curiously, when logging into the PHPMyAdmin through the installed cPanel, we can change those values there. This obviously isn't a long term solution as we can't give our writers cPanel / PHPMyAdmin access, but I mention it to help understand the whole picture.
What we tried
Error Logs - No Error logs (that we can find) show anything related to this issue.
Permissions - Permissions don't seem to affect this issue, as we can make changes to any value, as long as they don't include "select" or any variation of that name.
What I want to understand is why the cPanel PHPMyAdmin can make these changes, but not the manually installed one, or Joomla / OSE.