Why is GFCI Receptacle Tripping From Downstream Fluorescent LIght on Switch?
Well, this is embarrassing, but hopefully it helps others in the same situation. I used an old 3-way switch I had lying around and I mistakenly connected the ground wire to the other switch terminal rather than the ground terminal. So when I switched it to the off position current was leaking to ground and tripping the GFCI.
I wired it correctly and it's all working as it should.