I upgraded from an S8 to a U2 on launch and have been wearing it since. I recently noticed a red area on my wrist directly under the sensors. It doesn’t hurt, burn, or itch. My skin isn’t raised and feels normal to the touch. If you look closely the skin is “scaley” (and red, of course). Anybody else notice this?
I have bad pollen allergies. Sometimes, after hiking or SUP, I'll have issues with things getting trapped beneath the watch/band and my skin. My topical reactions often look like that. Be sure and (carefully) clean the underside of the watch to get anything off that might recontaminate.