*UPDATE*
I have used another Xs extensively for a period of time recently as well as display models at Best Buy, so this issue was tied just to the one phone I purchased. Unexplainable.
On a side note: I think i still slightly prefer my 8 Plus, but we won't go into that discussion
I posted earlier in the thread about feeling the same sensations in my hand with a XS that the OP had.
For me the sensations disappeared completely after 2-3 weeks, never to be felt again. Not sure if it was psychosomatic or what, but the problem just seemed to vanish one day. FWIW mine wasn't limited to it being plugged in.