The bug
When you have a clock which teleports an entity every game tick less than about 0.045 (value has changed) blocks, it looks raggedly.
This could relate to: MC-73980
How to reproduce
1. Summon an ArmorStand with NoGravity:1b
/summon ArmorStand ~ ~ ~ {NoGravity:1b}
2. Let a clock run this command every tick:
/tp @e[r=10,type=ArmorStand] ~ ~0.001 ~