Upon loading a world, redstone components update. The redstone may change based on an unloaded chunk, causeing it to turn off when it should be being powered by something in the unloaded chunk next to it. To reproduce: make a long line of Redstone with repeaters, power
one end, then stand at the other end and lower your render distance. Then reload the world. The redstone will turn off, then turn back on as you load the component powering it. This affects all redstone components that I am aware of, including pistons. It tends to break contraptions as one half may update while the other is unloaded, often sending redstone contraptions into a clock.