Two things:
1) Since you are unable to reproduce this error on MoodleCloud or qa.moodle.net, it appears to be a problem with your install of Moodle or server configuration. Or it might go back to what Tim said above. If you have done a normal new install of Moodle 3.6, this suggests some kind of problem on your server. Where do you host your Moodle?
2) In the above screenshot, I don't see any questions. Have you tried adding a true/false? If you have errors with adding any type of question, then my #1 seems to apply.
