Why does my screen turn off when I open the lid fully?

Over the last few months I have found that I cannot open my M1 Air lid more than 90 degrees, or the display turns itself off. To get the display back on I have to close, then reopen the lid. This is very reliable and gets the display back on every time, but recently I cant open the lid more than maybe 80 degrees.

I've noticed that if I place some magnets either side of the keyboad it affects/helps the problem. I've opened the underneath and reseated cable connections but that hasnt helped.

It feels like there is some mis-calibration with the lid open sensor but I cant find a decent answer on how an M1 Air senses how far open or closed the lid is.

I'm out of ideas. Feels like a cheap solution is possible but I'm not sure what that could be!