In my world I set up a 2 pistons attached to a tripwire. Both were set up symmetrically and they both powered fine but when I left the tripwire the right one deactivated whereas the left one was still activated with no apparent power. The piston stays activated until there is a nearby block update such as placing or destroying blocks. I can find no reason for this and as you can see from the picture there is really nothing else to give it power. As you can see in the third picture, the pistons works fine if place sideways. In picture 4 I built an identical model but joined both pistons at once, this caused both pistons to get stuck. This might have been the reason that only the left one was faulty in the last example as I attached that at a different time. (second). In picture 5 I have simple set up of the two pistons without the other pistons on the top. In this version they seem to work fine. In picture 6 I have set it up so the redstone is activated by a lever instead. As with picture 5 this works fine