I cloned the issue
BDS-5907 to MCPE because it happens here, too.
If it was wrong, feel free to delete one of the bug reports.
Observers get randomly stuck in a continuous powered state after a while. The red dot on the observer doesn't blink anymore, it is always on.
The corrupted observer doesn't give any redstone output, it just stays red and unusable.
The observer works normally in a different block, but placing it back results in the same behaviour immediately.
It is like if the block coordinate the observer sits in is "broken".
Putting other blocks in that space doesn't fix the block, after putting cobblestone in the space and rebuilding the observers the one observer is still broken.
Pushing it with a piston makes no change, too (Obs7.png, Obs8.png).
This happens regardless of what the observer was looking at, it already happened facing: other observers, pistons, redstone lamps
Obs3.png shows that this problem occurs even when changing direction inside the affected block coordinate.
Obs6.png shows which blocks are affected. After just 30 minutes of additional runtime of the dropper elevator even more blocks got corrupted.
The texture packs I am using have no influence on the behaviour. Due to the random occurence I don't know how to reproduce the issue.
This completely breaks every redstone machine with observers and makes the game unplayable for me, I rely on dropper elevators, item sorters and trident killers and all of them break at some point when observers are being used and updated. I don't want to lose 500 hours of work in this world.
Obs4.png shows the problem in Win10 Edition singleplayer (copied the map) with another observer 2 blocks below the previous affected one.