Affects Version/s: Minecraft 1.8.2-pre4, Minecraft 1.9, Minecraft 1.12.2, Minecraft 18w05a, Minecraft 1.13.1, 1.16, 20w51a
Fix Version/s: None
There are a number of things whose movement isn't based on tick speed, instead moving in real time. This means that when there is large tick lag, some things will behave oddly. There are 2 different categories of these:
1. Most of these just appear to move too fast, but actually don't. They will render as though in their new position, but are actually where they should be. Some of them can appear glitchy, sometimes appearing to snap back to their true location or disappearing for a while. Others appear perfectly normal:
2. Then there are the ones that actually do move based on real time, therefore becoming out-of-sync with other game objects if there is a large amount of tick lag:
Notably, minecarts with a player mounted work as they should, along with regular mob movement, status effect duration, and other things.
An easy way to induce tick lag with no frame lag is to summon a few entities and put "execute @e ~ ~ ~ testfor @e" on a clock. Be careful not to have too many, as too much lag can corrupt the world.