What might cause light to flash on for a second when turning on fan switch?

I have replaced 3 switches in one bathroom with smart switches. I did this a few weeks ago. I also just a few days ago had an electrician replace 15 switches (some on the same breaker as the bathroom) with some other smart switches. Just today I noticed in the bathroom, when I turn on the fan and turn it off, the lights over the sink flash for a second… If it then quickly turn on and off the fan over and over, it will continue to do this. I’ve read things where somehow this can be caused by LED, but none of the bulbs in the bathroom are LED. The ones flickering (I guess more of a flash since it is one flash) are incandescent.

Any thoughts? Tomorrow, I’m going to pull the switches out and check all the wiring, but thought I’d reach out since I am pretty sure I won’t find anything with the wiring in the bathroom.

I will add, it is possible this was a problem since the day I swapped the switches, but also possible it didn’t occur until after the other group of switches we’re replaced. The only thing that happened since the electrical installed the other switches is that the breaker these are on tripped once.

Thanks in advance!