Bit late to the party here, Its burn I just got the 245 after 1 week my wrist starting feeling a burning sensation, Swapped it to my other wrist when it was happening and I could feel the burning sensation immediately. left a tiny mark on the other wrist.
I got the 245 as an early Christmas gift and I also have had issues on both arms, non stop after wearing it just a couple weeks. As soon as I switched arms, it was better for a day or so, then got burns on the opposite arm as well. I'm thinking of contact support to see if they have an alternative band style that I can try to see if I am allergic to something in the band it came with.