Pick a task out of ammo (Doom Eternal)

I need to pass the level through the menu selection tasks.
When I start a mission. I have ammo and health from the previous battle.
0 BFG ammo, only the bullets of the gun.
Low HP.
I don't want to go through an easy mission just to get ammo for the BFG.
Why do I have to complete another mission for ammunition.
Why starting level through the choice tasks, the bullets do not give a right?
How to fix this bug?