Welcome to the community forum. 
I would suggest you check if there is a Fairphone Angel nearby:
If you’re lucky, s/he might be willing to literally take it in her or his hands. Given you already performed a factory reset, there’s the advantage of not having to rescue data or the like, this makes testing easier.
Alternatively, you might want to temporarily swap modules (for testing) with another FP2 owner if you know one, especially the battery and the bottom module would be candidates.