Another thing to check is the shutter button, some of these have failed (or been poorly adjusted from factory). Take as many pictures as you can and get the feel of it, if you’re finding that it doesn’t always fire or you sometimes have to press harder than you expect, you’re probably not imagining it and it probably does have a fault.
I had this on two different XP3’s, both from factory, I ignored it on one (and later sold it on) but the other eventually got worse to the point where Fuji replaced the top plate under guarantee - since then no problem.