Yes, this seems a puzzle that may take a little testing to clear. But it doesn't involve a whole big bunch of the wiring, so that makes it a bit easier.
First is a small point on what you are dealing with as the GFCI tells us different things than a normal breaker. The normal breaker will trip when too much current is flowing and it heats up and trip.
But the GFCI is a different type of safety which is designed to cut off power very quickly IF it finds there is power flowing in the wrong way and going to ground. Fault to ground might be a better name as it looks for things like power going out a bare wire and through us to ground! It is meant to work so quickly that we don't get a major shock!
So changing to a 20 amp was not all that dangerous as the original breaker which senses the amount of current was still the same 15 amp breaker at the load center. Just that one specific outlet was going to be slower to melt down, which is okay, even though rated more than expected.
But I am going to guess there is a problem in the circuit, at the GFCI or beyond that is letting some power leak to ground and that may be some temporary thing. Temporary faults can be harder to find because they do change, so we sometimes have to work the problem real slow and steady .
Looking at this drawing, I think you said the breaker is not tripping but the GFCI is, meaning the problem is something at the GFCI outlet or one of the others "downstream" / further away from the load center. The reason they put GFCI on these outlets is that they all are close to places where we might be wet and handle the electrical items plugged in them.
So what the GRFCI tripping is telling you is that there is some point along those outlets where the power is not staying where it should and is leaking to ground. Since it is come and go, it may be something that you plug into one outlet that is not working right. Hairdryers are really good at doing that but it may be something that trips when that item is plugged and and then doesn't trip when everything is unplugged.
Of course it could be a problem in the wiring but that is less likely to come and go than an item with some small defect which is plugged in and trips the GFCI but then unplugged when you are looking for trouble. So if it is tripping now, look what is plugged in and try unplugging one item at a time until it stops tripping! If you get all these outlet empty and it still trips, look very carefully at each outlet for any signs of something out of place and if not spotting anything, try disconnecting some of the wire to some of the outlets to see where it stops tripping!
That's where slow and steady has to be done as it is meant to work really quick to save us if we drop the hairdryer in the sink and try to grab it! So that means a splash of water in the outlet may trip it and then dry out and leave us going silly trying to find it like a ghost! But while it won't reset right now, that's a good time to find the ghost!
Maybe something gets shoved up against an outlet and then it's gone like a ghost? Sorry, we have to look really carefully to find a ghost!
No power to some outlets
Linear Mode
