This may stem from MC-226243, but when the data of a goat is modified (excluding modifying rotation), it rotates clockwise about its y axis. Here is the summon command I used:

How to reproduce

1. Summon a goat

   /summon minecraft:goat ~ ~1.5 ~ {NoAI:1b,Silent:1b,PersistenceRequired:1b,Invulnerable:1b,OnGround:1b,Rotation:[90f]}

2. Use data merge to change a tag

   /data merge entity [UUID] {Tags:["tag1"]}

   /data merge entity [UUID] {Tags:["tag2"]}

   /data merge entity [UUID] {Tags:["tag3"]}

3. Observe how the rotation changes, even though it shouldn't. This can be done more easily through using hitboxes via F3+B.