On Sat, 05 Nov 2016 08:56:45 -0400, Mr.E wrote:


A feed through installation would allow a downcircuit load to pull
through the GFCI and an internal failure in the GFCI could cause this.
--
Mr.E

That's true too and one more possibility. Maybe it was not the GFI at
all, but a mouse chewed tthe wires real close to that box.