In 1.15.1, there's a possibility in the setup below that the 2t(2 redstone tick, or 4 game tick) repeater could emit a pulse with wrong length. It might emit a 1t(2gt) pulse instead of 2t(4gt). What I supposed to see: everytime when I trigger this setup and reload these chunks, I will get a 2t repeater emiting stable 4gt length pulse

The possibility of the bug happening is positively related to the render distance and negatively related to the max framerate. You can easily trigger this bug with framerate set to 10 or render distance set to 32, but can't when framerate set to 120 and render distance set to 2. 60fps + 12view distance might be a good config to check its randomness. I think it's relative to the performance of your PC

Here's a video of this bug: https://youtu.be/ie2Y5HRbgnk. The sample world is in the attachment

This bug could mess up stuffs due to the random wrong behavior of the repeater when someone leave and unload a chunk, and then reload the chunk. For example, logging out from a server or entering another dimension

This bug also happens in 1.14.4, but not in 1.13.2 and below. It might due to the chunk unloading system change

2020/8/30 updated for 1.16.2: This bug still exists but the length of the pulse the repeater emits has changed to 3gt instead of 2gt, which might be the result of the fix of MC-172307. But the piston still losses its block