Raindrops will seemingly disappear or change position mid-fall. This does not seem to occur when the tick rate is 0 and is hard to notice with tick rate 3+, so the easiest way to repro is to run /weather rain and /tick rate 1 and watch the rain for a while. (Do not move your player while doing so to avoid triggering the related MC-187442.)

For a video, please see rain_bug.mp4.