The horizontal rotation (y_rotation) of zombie and skeleton that spawn by command will not update until the mob is aggro at something but the mob itself can still move their head like normal.
This seems to affect everything that involved rotation
/data get entity <Skeleton> Rotation
/particle happy_villager ^ ^ ^2
....@s[y_rotation=10..90]....
etc.This is only happening with horizontal rotation, the vertical rotation still acts like normal.
Is this still an issue in the most recent versions (currently that is 1.13.2, or the latest snapshot 19w14a) of Minecraft? If so, please update the affected versions and help us keeping this ticket updated from time to time. If you are the owner/reporter of this ticket, you can modify the affected version(s) yourself.