I am still getting to grips with this, so I might be missing something but I think I have spotted the following problem. (And thanks to Dani Palou for all the help he has given me so far.)
The problem is that some question types may, or may not, work in the mobile app, depending on what options are set. There is an example in standard Moodle with the essay question type:
This is good (And the code that does it is here https://github.com/moodlehq/moodlemobile2/blob/e10e0de0107101c42c3432b09fbaa73498be54af/src/addon/qtype/essay/component/addon-qtype-essay.html#L18). The problem comes with other question types, for example:
The problem here is that although we have displayed a warning in the same way that the core essay qtype does, the check button is still present. And, since the check button is rendered by the question behaviour, not the question type, this not not something we can control in our plugin.
Note that, on the summary page at the end of the quiz, a different warning mechanism is used:
The code for that is here: https://github.com/moodlehq/moodlemobile2/blob/e10e0de0107101c42c3432b09fbaa73498be54af/src/addon/qtype/essay/providers/handler.ts#L59, and you can see that here, our plugin has been able to hook into the core mechanism.
I have some thoughts about how to fix this, but I have to go to a meeting now. Will post again later, but for now, I have only managed to describe the problem.