To reproduce:

• /summon minecraft:goat ~ ~ ~ {NoAI:1,Rotation:[90f,0f]}
• The rotation is not towards west as for other entities but still to south.

When disabling the ai of a goat that is not looking south and reloading the chunk it will again look to the south.

• Have a goat that is not looking south nearby
• /data merge entity @e[type=minecraft:goat,distance=0..3,limit=1] {NoAI:1}
• save and quit, reload the world
• its looking southwards

Both issues do only happen for goats, other entities have the correct rotation so i think it is a bug.