When an armor stand is on the ground, updating its rotation via /tp sometimes causes it to twitch and then remain facing the same direction visually.

To test:

1. /summon armor_stand ~ ~ ~
2. From chat: /tp @e[type=armor_stand,c=1] ~ ~ ~ ~90 ~
3. Repeat step 2 from your chat over and over.
4. Notice that sometimes the armor stand fails to rotate visually.