Always on stopped working - why and how do I fix it please

Had my series 8 since April. I like my watch face to be always on. It's stopped working and doesn't even come on when I turn my wrist - I have to tap the screen. So frustrated. Tried settings, and Always On is on. Tried turning off the watch on back on. Tried turning always off and leaving it then putting it back on.

Why is it so difficult and why isn't it working?