Updating a Skeleton's main-hand, through API or through vanilla commands, fails to update their weapon goals resulting in them becoming 'passive' or maintaining a melee goal when they should prefer a ranged attack goal. 

Steps to reproduce:

1. Summon a skeleton (`/summon skeleton`)
2. Replace their main-hand weapon via command (`/item replace entity @n[type=skeleton] weapon with iron_sword`
3. If not already; enter survival mode to allow the skeleton to be aggressive.
4. The skeleton should become passive and will no longer target you.

Note: this does also work with a skeleton summoned with a sword or no item in their hand and replacing the item with a bow; in this instance the skeleton remains hostile and will just beat you with the bow instead of shooting it.