I’d like a solution to this bug, far as i can tell the reason you sometimes receive less minerals than required to complete the mission is because mining drones returning with cargo if redirected before cargo is returned will fill from zero cargo again losing the little cargo you already have.
This should be testable and fine solution to the Bandine issue.
In all seriousness, though, don’t wait for CCP to provide a solution. This has been bugged for going on a year now. Provide your own immediate solution. Don’t use mining drones. Mining lasers and strip miners are much faster anyway.
Having said that, at a minimum, CCP at least needs to provide a warning in the mission description not to use mining drones, not that new players would read the mission details anyway…