Are new items like backpacks, etc... automatic added to loot tables or?
How I can check that?
Because in this wipe, players was getting minigun from locked crates, but they complaining about not finding large backpacks.

New items are not added to your LootTables.json. If a container is "Enabled": false then it will be vanilla loot, the plugin wont touch it. You can check NamesList.json for all the items.