EDIT 2: I just tested, and when pistons get stuck, they act like solid/opaque blocks, meaning you can send a pulse through them and have a repeater pick up the signal on the other end, which doesn't normally happen! this means that this bug is actually the same thing as
MCPE-17304! I think the mods should merge the 2 issues, since they are one and the same.
EDIT: Apparently this also affects droppers/dispensers as well. See: https://redd.it/55pbt1
So I tried to activate a random sticky piston in my world and it just wouldn't activate, even after giving it block updates, breaking the block above the piston that it was supposed to push, breaking and moving the lever that was supposed to power it, placing a redstone block next to it, and trying all sorts of ways to power it. After relogging, the piston started working again. I have no idea what caused this bug or how to reproduce it, but luckily I was smart enough to start recording when the bug happened. It happened again later on to the same piston, but I could never reproduce it consistently or with any other pistons in my world. Note that I never broke the piston that was behaving weirdly.
I'm sorry that this bug report is so vague, but I honestly have no idea why this happened or how to reproduce it. If anyone has any idea why this might have happened, please let me know... I haven't got a clue as to what would cause this to happen, other than improper world-loading, in which case this might be related to
MCPE-13608 and/or MCPE-14233.