In my case the problem source was a missing question type.
There were existing questions with the missing question type, then later likely the question type plugin was deleted. This is why the error appeared.
Using Moodle v3.5.1+
In my case the problem source was a missing question type.
There were existing questions with the missing question type, then later likely the question type plugin was deleted. This is why the error appeared.
Using Moodle v3.5.1+