I am a software engineer (at least I would like to think so
) a system maintenance in this scenario could mean they would have to update their logic to re-calculate scores. Yes this is comparatively a small change. Once they finalize their logic and complete development of their software code, they would update current profiles (in batches based on current CRS score or date time of profile creation etc..) validate their changes and post it. They could do it in one go but I believe they do in batches as we see a few people saying their scores are updated and others do not have theirs. Doing it in batches would also give them flexibility of identifying any bug at an earlier stage so they can fix it.
They could also be doing some system cleanup, upgrade or what not when they say maintenance.
Any other thoughts?