The bug
The /data remove command can't remove the NBT CustomName.
How to reproduce
Type this command:
/summon spider ~ ~ ~ {CustomName:"{\"text\":\"Grumm\"}"}→ ✔ You can see its name by looking at it
Type this command:
/data remove entity @e[type=spider,limit=1,sort=nearest] CustomName→ ❌ Its name should be removed, but it isn't
Expected behavior
The name of the entity should be able to be removed using the /data remove command.
Does reloading the world (leave and enter) fix it?