All mob motions is jittery - whether walking along or flying or bobbing in the water. They appear to moving at about 1/2 speed. When villagers bob in the water, they appear to be briefly standing on the surface.

Arrows appear to travel about half as far as they should, and the variation in range is far more than expected - some will go almost as far as I'd expect, others drop short drastically.

My movement and updates appear to be unaffected.  There are no chunk updates and not an excessive amount of entities nearby.

I've tried this on both a linux client and windows client on different machines and observed the same issue

When I switch back to use pre-4 on the same server, everything is as expected.