I’d suggest taking a ‘screenshot’ of all the router stats when it isn’t
happening to start with ... to have baseline as such. Then have the suspect switched on at an agreed time and then watch the stats.
Some sources don’t kick straight in either, they need while ‘warm up’.
If you get a positive result .... low SNR, heavy corrected errors ... turn the suspect off again, see if things stabilise on the stats, then see if you can repeat the issue by switching it back on.
I believe you have said it doesn’t cause you any service affecting problems. More evidence that it might be nigh on impossible to locate.
like the article seems to suggest their TV did
I had read this as the faulty telly in the article was causing loss of sync to those nearby. Prompting my comment of why it took so long to find ... it being a fairly black and white case.