Board Thread:Unanswered Questions/@comment-25074480-20150920011517/@comment-25045164-20150920013918

Reimbursement comes from research. As you know, everytime you're done with a mission, the game will reward you some research progress for your items. What if the game finds that none of your items is viable for additional progress due to all of them have already reached 100% research progress at their respective levels? The bonus is then converted into credits, hence the reimbursement.