I've been using LagGoggles on my Modern Skyblock 3 Departed world; and the entry in general on top for the FPS scan (meaning, the functions mostly responsible for lowering the FPS) is
me.ichun.mods.ichunutil.client.entity.EntityLatchedRenderer, with a huge lead.

For instance:

5675 ns/F me.ichun.mods.ichunutil.client.entity.EntityLatchedRenderer
167 ns/F BlackHoleTank
96 ns/F TileContResT2
...

Note that this is FPS-related, and not TPS.

So I've been asking myself, could it be that either some mod is abusing this function; or that the function itself is implemented in a way to produce overhead?

I tired to sift out the mods that use iChunUtil via https://github.com/daviddrysdale/jnm but that doesn't really work, or I'm missing something. But maybe you've got a good idea which mods use it.

This is obviously low priority, I just thought you might want to know.

Also having the same problem, mine's at 13691 ns/F, EntityHat is my second-highest tho, at 4494 ns/F.
I've had limited success limiting this by turning off mobs spawning with hats.

If anyone playing MS3 is still having this issue the mod can be removed completely from the install as it does not have any active dependents.

I'm not sure what's causing this issue but I have identified that I'm accidentally spawning new EntityLatchedRenderers when the game is paused so I've fixed that.

I've also added a new config to disable them spawning entirely (I hope), not a definitive solution but that'll come only in 1.13.

These changes will be in the 7.2.0 update of iChunUtil.

Also having this issue in MS3. When I try to transport to the entity, it says it no longer exists but the FPS lag still exists.