Dear Joe, has the issue been repaired? As, a technician, I experienced a fault, similar to this, in a farmhouse,
once in Essex, putting aside some very technical, reasons, consider keeping it to any simple causes, as well.
You have an intermittent fault, causing flickering, and "brown outs", i.e. not completely off, or trip of breaker.
Is this happening, in wet weather? In the farmhouse, rainwater, on a broken light fixture, did the short circuit.
It can be a general property maintenance issue, suggest checking, for any rainwater ingress, or a pipe drips.
Could also, be caused by a bathroom remodel, where fitter has not waterproofed, or capped old wiring right.