That killing of the cards sounds anecdotal, though I don't know exactly what else they were doing besides undervolting to kill their cards. And, the article I'm talking about pre-dates the mining craze.
https://www.tomshardware.com/reviews/msi-afterburner-undervolt-radeon-r9-fury,4425.html
That aside, I don't think undervolting is the solution - things are running way too hot, enough that artifacting is occurring. This is a 180W card, and so cooling it shouldn't be that difficult (we're not talking Fury X or Vega 64 here). Something's wrong, but that's why temperature (and probably fan speed) measurements need to be taken.
And insufficient cooling can be the problem and still warm up the room - heat does diffuse, depending on the size of the room, of course. Further, some cooling, while not enough for the card, can still push heat out into the room enough to be noticed.
Get temperature measurements and fan speed measurements over time.
EDIT: also, what's the normal temperature in the room when the computer's not on?