My guess is the bulbs — some LED bulbs are marked dimmable; others aren't. Try replacing the bulbs in a fixture and see if that fixes it. (We have the same issue with a new house where we didn't choose the existing LED lights.)

Thanks. I have check and changed bulbs. I’ll look into the dimmer. I do wonder whether fluctuations in the power supply might mess with the bulbs when dimmed

In my experience it's always incompatibility between the lights and the dimmer.

Yes this happened to us and we changed the bulbs and the issue was resolved - we too thought it was the wiring and almost paid for an electrician visit

@la_la Girl: "we changed the bulbs and the issue was resolved"

Only one of her three types of lights has replaceable bulbs.