sometimes observers don't produce pulse signals when pushed together by pistons. To reproduce, get these blocks:
2 observers
11 redstone dust
1 sticky piston
2 solid blocks (I used white concrete)
1 redstone lamp
build the contraption like provided below, and put a redstone dust in the middle of the two observers. There, you get two inactive observers.
comparison between regular and bugged on the left.
Edit: Maybe this is WAI, but I really don't get why the observers don't observer the other observing observer. When i place the redstone, they both update, and when the piston pushes, they should both get updated again. Is it because it happens too fast that they don't update?