Normally sticky pistons unstick to their blocks if they are 1-tick or 0-tick powered.

-make a suspended redstone line on solid blocks
-put a couple of pistons below it, 1 block spaced apart from each other
-hook them to any 1-tick source, such as an observer, clock or monostable
-power them and notice that some pistons never unstick.

patterns may differ depending from where you power them, sometimes the bug may not appear, so try different locations.

In my attachement I powered this line only twice, and as you can see, only the first 2 pistons behaved properly, unsticking.

Temporary fix is to place another piston right next to them, or power from another side