The bug

Pillagers summoned with loaded crossbows will still load their already loaded crossbows instead of automatically shooting it. This can also happen if the player save and quit the world while their is a pillager with a loaded crossbow.

To reproduce

1. Spawn a pillager
2. Run

    /summon pillager ~ ~ ~ {HandItems:[{id:crossbow,Count:1b, tag:{ChargedProjectiles:[{id:"arrow",Count:1b}],Charged:1b}}]} 

3. Switch gamemode to survival

Alternative

1. Spawn a pillager
2. Go to survival, and wait for the pillager to load it's crossbow
3. Save and quit to title
4. Re-enter the world
   → The pillager "loads" pre-loaded crossbow

Notes: This happens if the player save and quit to title or summoning them with commands.