The Bug

Upon pausing the game in singleplayer, the positions and rotations of particles, entities and block entities can appear offset from where they were on the frame before pausing. This is somewhat easier to notice at lower tick rates.

pause bug 23w45a.mp4

This may or may not be the manifestation of the potential code problem described in MC-142160, I don't know enough about what that function does to say for sure. If it is the same issue that ticket should probably be resolved as a duplicate of this one.

Reproduction

This bug can be reproduced using the method in the video. Another interesting way to do it is to run the following:

1. /summon minecraft:small_fireball ~ ~1 ~
2. /ride @s mount @e[type=minecraft:small_fireball,limit=1,sort=nearest]
3. /tick rate 1
4. Enter third-person view and move your camera. Notice how your horizontal mouse input lags so that your facing direction aligns with the orientation of your character.
5. Swivel your mouse and pause and unpause the game while your character is turning.
   Your view angle changes abruptly when pausing and unpausing.
6. (Optional) Return things to normalcy with /tick rate 20 and /kill @e[type=minecraft:small_fireball,limit=1,sort=nearest]

I made a YouTube video demonstrating this reproduction method.