Burn mark from 7s solar

So that's a new one. I bought the 7s when it first came out. No problems, only updated the firmware when I got it, don't use O2 measurement. Took it off to charge it today, and noticed I have a burn mark where one of the sensor sits: when worn left then away from the hand. I had the same problem with a fitbit charge 2 ages ago, and Fitbit replaced it without problems. But Garmin here is ***: They first want the watch back, then they'll send out a new one, which I can't do right now due to training programme and other stuff. Oh great. Anyone with a similar experience?