We had similar issues with GFCI outlets and use Eagle (Cooper Products) but it is always with outlets that are outside under "weather proof" covers. I believe it is a moisture problem and all outside GFCI outlets are candidates for this problem. I takes very little moisture on a printed circuit board with line voltage to cause arcing and carbon traces that only agravte the situation further until there is the real possibility of a fire. We had a similar situation and have quit placing GFCi receptacles outside. We always put the protective device ( GFCI Receptacle or a GFCI breaker) in an interior dry environment and then wire downstream to the outside receptacle for protection of it. Weather proof covers are seldom weather proof unless they are periodically checked for proper sealing against the surface they are installed on. Even then with quick temperature changes there is the possibility of condensation forming on the circuits inside the outlet.

That's my 2 cents...