I had a much worse version of that at the beginning of my PMR journey. Which went away with prednisone. I had originally thought it was carpal tunnel, but Dr. Google informed me it was cubital tunnel in my case. It only happened while sleeping and I was able to get rid of it by consciously keeping my arm straight at night. Which is hard to do while you’re asleep, but it worked. Of course, since this is emerging while you’re tapering, it sounds like a situation to run by your doctor if it persists.