I'm playing right now in my sony xperia c and this rarely happens when i'm making a flying machine without using observer blocks. The bottom piston doesn't respond quickly when the top piston pulls the slime block sticked to the bottom piston that the bottom piston touched the redstone block. What i mean is the top piston responds quickly while the bottom doesn't. A rare bug.
Proof:https://youtu.be/ZxKmv4YoClE