After updating to 13.21 and doing a treadmill run, my watch now has a 1 pixel wide vertical blue line down the very centre of the screen.
This is only visible with a "black" screen and isn't there when the screen is white or any other colour.
I'm thinking this is actually a software / firmware issue but as I've only had the watch a month I can send it back to the reseller if its something more serious than that. As I'm not seeing an avalanche of similar posts - should I just wait for the next firware update or send it back now?