I think this has started as of one of the last patches, but it could be as "old" as the Valley of the Zeke update.
By default, Fixer's Supply Bag has 4 uses.
Efficiency (3rd Passive) gives +25% Ammo (1 Use),
Fourth of July (C8R1) gives +1 Supply Bag Uses.
One for the Road (C5R1) takes 25% Ammo (1 Use) away,
3 in 1 (C9R4) takes 1 Use away.
With Efficiency, Fourth of July, and One for the Road or 3 in 1, the Supply Bags should have 5 uses.
However, currently, they still only have 4.
This is especially relevant with Armory (C1R2), which has a 20% chance of refunding an Equipment to the user and Fixer, as we're now guaranteed to go net-negative over a long enough period of time.
Would like to know if this was purposefully changed (or if they took away RNG stacking in our favour for every failure), or a bug.
Cheers.