Since guardians and elder guardians are mostly ignored like any other mobs, they have broken animations as of 1.13.0.6 Beta. Details are shown below:

Guardians/Elder Guardians in water

*Spikes don't retract when swimming.

*Tail seems to be jittering from whether it should move fast or slow.

Guardians/Elder Guardians in land

*Spikes have a weird glitchy retract and expand animations on land.

*Tail sways very slow when they are flopping.

Rotation

Guardians have a weird vertical rotation, the rotation has been changed in 1.13.0.6 Beta. They now rotate in a top arc clockwise when vertically rotation to attack a player/squid, they rotate in a bottom arc clockwise vertically. The laser beam becomes offset, and half of the guardian's body is clipping through a wall.