This might just be a random unseen bit of dirt, but I had a persistent "! Lens Error" with the 27mm, even after removing and replacing the lens five times, and checking that all the contacts and the mount were good. Lens is fine on an X-E1. On startup on the X-Pro2, the rear display flashed on and off about 30 times over a period of 20 secs (with camera unresponsive), reporting the aperture as F1.0, before finally giving up and saying "! Lens Error". Repeated 6 times, removing and replacing lens. It was only when I swapped to another lens on the X-Pro2 and then back to the 27mm that the problem disappeared, and I haven’t replicated it in the last hour.
Got to say that I'm kindof enjoying this "Where's Wally" of possible bugs. Masochistic, but fun.