by Leon Stringer.
It looks like this site has been upgraded using Softaculous. Softaculous is notorious for breaking sites on upgrade because it leaves behind the source code files that get removed between Moodle versions ("Do NOT copy new files over the old files"). The problem you've reported – and are working around with $CFG->modchooserdefault – is exactly this kind of problem.
The fix is to ensure only the source code files for the current Moodle version are present, try these steps. Some people (one, two) have suggested that you can open a support ticket with Softaculous and they'll fix the upgrade.