Some magazine followers barely "set" the bolt catch so the slightest movement sends that mousetrap home. Have you recently changed magazines. Also the poor little bolt stop does wear out. Look at the corner where it catches the bolt. It started life as a square. The same magazine issues will cause the catch to die early.
Same here... problem the follower like the one on the right are nowhere to be found. There are "USGI" followers for sale out there, but nowhere near like the same.The first and only time i ever got garand thumb was from single loading my m1a with a magazine like the one one the left.