While I was improving the match rules in a pattern match questiontype I noticed that suddenly the atto editor didn't load and the collapsed menus were not clickable any more. That is I can't expand any of the sections in the question type editing form (for example 'Multiple Tries, 'Tags' or other specific for this particular qtype).
When I reload (F5) the form, the web dev console of firefox shows a 'TypeError: this.div is null' error. See it below:
moodle-core-event: Global event published: FORM_ERROR yui_combo.php:5828:21
moodle-core-event: Global event published: BLOCK_CONTENT_UPDATED yui_combo.php:5828:21
I tried to solve the issue purging caches, changing the theme, changing the atto editor and even changing the default language. I made one change at a time without success.
It's weird that, if I clone/copy the question I can open the new question and all seems to work well. A reload (F5) in the cloned question doesn't display the 'TypeError: this.div is null' error mentioned before however the web dev console of firefox shows a warning on:
Synchronous XMLHttpRequest on the main thread is deprecated because of its detrimental effects to the end user's experience. For more help http://xhr.spec.whatwg.org/
I'm afraid that I'm going to face the issue again but I have no idea how to fix it or about what can cause it. I refer the issue to 'Quiz' and 'Forms Library' components because I only found it while working in a [Pattern Match] Quiz form.
I'd appreciate your help to fix it.