Attempting any multiple choice question in the App gives the error message "An error occured while reading the questions. Please attempt this quiz in a web browser".
I rebuilt our site from scratch yesterday using Moodle 3.9.2, however I think it was only after upgrading to 3.9.3. that the error appeared.
Matching, short answer and True/False questions all work ok. Multiple choice questions work in a web browser as expected.