when a comparator is placed in a particular arrangement (attached) it can jam in the on position, occasionally giving false readings when it is next used.

in the screenshot, when the gold button is pressed, it behaves normally, however when the diamond button is pressed, it jams powered as pictured. this will only reset if a redstone signal with a value less than 15 is sent through the comparator.

notes:
the green box is a chunk boundary.
the red green and blue is X Y and Z
the lit up comparator is the problem comparator
repeater is on 2 ticks (2nd position)
issue is in both singleplayer and multiplayer