aritech system; issues with tamper alarm

Hi; we have an aritech system in a house we bought a couple of years ago, and on which the previous owner had let the maintenance contract lapse about five years earlier.

The alarm was fairly well behaved until christmas day, when it went off a couple of times when we were out of the house, and again on stephen's day; so the next day i took the covers off some of the sensors and junction boxes on the faulting zone to see if there was any issue (the zone includes the back door, but it's not an entry/exit zone); they all looked OK, bar an earwig living in one of the junction boxes, and i put the covers back on.
However, now when i set the alarm - or even just use the keypad to view the logs - it arms and disarms without error; but after i disarm the alarm, as soon as we open the back door, the alarm goes off with a 00 Lid tamper/panel tamper error (just on the first attempt to open the back door after using the keypad). I've since opened the panel and ensured the tamper spring is engaging correctly, but this didn't resolve the issue.

should i be seeing a panel tamper error on triggering of a zone even when the alarm is not armed?
i get access denied on what i've been told is the factory engineers code for the alarm.