Looks like I've had a 'moment' and not released it. Also seems that the M3.5 version is missing one commit. I'll get around to this at some point. You could try out the code as it stands here: github.com/gjb2048/moodle-format_topcoll/commits/MOODLE_35 - but be aware that as its missing a commit but it will be the same version then when I do release on Moodle dot org you'll have to manually update.
But if you have a test server that does not matter then please see if it actually fixes the problem.
Or you could upgrade to Moodle 3.6 or 3.7.