PHP8.0 issue in interpret_subcontents - with a particular question

[nwp90]

[11-Apr-2022 08:13:54 Pacific/Auckland] PHP Warning: foreach() argument must be of type array|object, null given in /d1/srv/moodle/otagounifom/moodle/question/type/pmatch/pmatch/interpreter.php on
line 178
[11-Apr-2022 08:13:54 Pacific/Auckland] Database transaction aborted automatically in /d1/srv/moodle/otagounifom/moodle/mod/quiz/processattempt.php
[11-Apr-2022 08:13:54 Pacific/Auckland] Default exception handler: An error occurred while processing your responses (Coding error detected, it must be fixed by a programmer: Oops. You called matches for an expression that is not valid. You should call is_valid first. Interpreter error :Non recognized sub content in code fragment "match_mw (less*|smal".). Click continue to return to the page you were on and try again. Debug:
Error code: errorprocessingresponses

• line 2479 of /mod/quiz/attemptlib.php: moodle_exception thrown
• line 89 of /mod/quiz/processattempt.php: call to quiz_attempt->process_attempt()

Not currently clear what has caused this - maybe an invalid match expression?

[timhunt]

I can't reproduce the error just by copying the bit of pmatch expression from the error message into a new question.

To progress this, we will need more information. Can you find the question that triggered this error? (Try searching in the question_answers table in the database for match_mw (less*| or something.

If you find the question, can you edit and/or preview it? If so, can you reproduce the error?

[nwp90]

We're not yet able to reliably reproduce it either; working on it.