I believe you are experiencing the same bug as I - which I think the game is still counting progress towards the Mecha quests (in my case, the collect 75 globes repeatable was the last one I had active).
Although the Mecha quests are no longer available and do not appear in our quest tab, the quest system is still awarding progress but no actual loot chests.
- Which Mecha quest did you last have active?
- Is this only occurring after a win? All the repeatable Mecha quests required winning.