Follow up ... a way to 'safely' make the conversions ...
Put site in maintenance mode via CLI script in code/admin/cli/
php maintenance.php --enable
Clone database (for example purpose it's currently called 'moodledb') and restore it to a new database with a different name ... like 'moodledbssl'. It has/uses the same credentials as the original DB.
In config.php file copy the DB name line and paste it back in just below the DB name line you copied. Change the copied DB line to 'moodledbssl'.
Original line:
$CFG->dbname = 'moodledb';
Copied line:
$CFG->dbname = 'moodledbssl';
Comment out the original DB name line by adding '//' in front of that line.
// $CFG->dbname = 'moodledb';
Now try the replace conversion tool.
Test site ... go to course that had the issue.
Works? If yes ..
edit config.php take out the comment for the original DB and comment out the 'moodledbssl' line.
Run the conversion tool with greater confidence now that it will work.
Might leave the commented out moodledbssl line for later/other 'testing' ... or 'mass' types of actions.
Above process used 4-5 years ago without issue.
Obviously, no one but OP can be responsible for 'typo's' when providing parameters for conversion.
'SoS', Ken