Hi,
Some days (weeks) ago, we had a problem on Moodle 3.7.3 for a student, in a time limit quiz with auto-submission : the submission was auto-submitted after 11 minutes, on a 20 minutes quiz.
After investigating and testing also with 3.8, i've created MDL-67512 with details on this. For french reading people, you can read this discussion.
Séverin