Anything moving while opening menu screen cause this
From MC-118009 by @unknown:
Summary:
When the game is paused while the player is moving, the background goes jittery and "vibrates". Note this does not happen while the player is stationary.
How to replicate:
Simply open a single player world in Minecraft 1.12-pre6 and move around. This could be through walking, sprinting, flying, looking around/rotating or jumping. If you pause the game during movement, you will experience it.
N.B. If you aren't experiencing the bug it may either only happen for me, the bug was fixed or certain conditions weren't filled to replicate the bug.
It might also not affect only 1.12-pre6, but other versions as well.
Linked issues
is duplicated by 25
MC-118004
Opening Command Block while Moving Makes Screen Shake
Resolved
MC-118005
Incorrect entity movement in "Game clock stop state"
Resolved
MC-118006
The background of the pause window stutters if you pause while something in your view is moving
Resolved
MC-118007
Weird pause bug
Resolved
MC-118009
Jittery movement caused when game is paused
Resolved
20 more links
migrated
Relates to MC-118001