Shot in the dark but
@vassallon suggestion actually came up for one of our customers; they had some 'different' security monitoring equipment that, when the alarm's scheduled night mode came on, would make the nearby APs act up very strangely. I don't know the details; it wasn't my ticket.
I know the nearby APs adjusted power settings to max every night and didn't seem to recalibrate them after the security equipment was shut down in the mornings. And client signal was worse in the mornings but got better with a reboot.
This was 2-3 years ago so maybe firmware updates would have made a difference since then. And support definitely has access to information that can't be viewed in the dashboard; I have wishes entered to get more of that into the event logging.