Why is my BAND V2 flashing red while on charger or immediately when placed on the arm?

If the haptic and red LED feedback lasts for about 40 seconds, then it is likely a Hardware Error.

Infrequently, a BAND V2 device may encounter a hardware error that causes that device to work improperly. The best indication that a BAND V2 is not working properly would be a noticeable flashing red LED while on charger or immediately when placed on body.

Please see this support article for more details.