GFCI's will get "weak" and become overly sensitive. I have seen them new out of the box that were unusable because they would trip after a few minutes. I bought a "portable" generator (new) that had two GFCI receptacles. You could start it up and run it and in a few minutes it would trip both of them (randomly) with nothing plugged in. I have had them get weak in my shop and start tripping.
I would start by installing a new, good quality GFCI receptacle. The new ones will not let you press and latch the reset unless the wiring is correct, after you install it.
Charles
