Due to MC-147818, chunks are not loaded by redstone lines. But instead of just updating to the new state of the redstone line once the chunk is loaded, it apparently keeps a list of changes that would have had to be done, had the chunk been loaded, and then executes them all at once as soon as the chunk is loaded.

If for example a long redstone+repeater line leads out of the render distance and it's toggled on and off without loading the repeater in the attached screenshot, that repeater will instantly turn on and off again once it's loaded, creating a zero-tick pulse. (The existence of zero-tick pulses is tracked in MC-8328, here it's just an easy way to visualise this bug.)