I doubt I can offer a simple fix. It's not an issue we experience here. It sounds like Respondus does not (always? sometimes?) work properly with the Ace editor. But can you first confirm please:
- Are you in fact using Respondus?
- Do the problems occur with normal (non-locked-down) browsers?
- If you change the Respondus settings to allow access to coderunner.org.nz, do you get the same problems when you attempt quizzes there, e.g. https://coderunner.org.nz/mod/page/view.php?id=549
I think you will need to track down exactly when the problem does and does not occur. Please report any findings.
Respondus traps every key press and disallows some. It may also be trapping and disallowing some output to the screen that is used by the Ace editor. If so, there is unlikely to be a solution: you might have to turn off the Ace editor during exams as discussed earlier in this thread.