You already know the answer:
iso problem feedback is on-topic.
real bugs are on-topic. (though should be explained in detail in the linked bug report, not here)
Both of those are the original subject of the thread.
Helping users diagnose problems with their own systems is off-topic. They hijack the discussion and turn iso feedback into one-person’s-personal-support thread. That’s just plain rude to everybody else.
You CAN discuss it: Simply move new subjects or side-conversations to PM or to a new topic. The “New Topic” button is not difficult to use. Once you resolve whatever the aside or diversion is, bring back the result on-topic with a simple summary.