That mildew smell is from the mop pad, not the vacuum.

Probably. The most common cause is leaving a damp mop pad attached or storing the robot with a wet tank.

Mildew loves dark, warm, moist places — exactly what your robot’s mop compartment is after a cleaning cycle. The pad gets damp, you forget to remove it, and a day later it smells like a basement. Same goes for the water tank if you leave leftover water sitting for weeks.

Fix: Remove the mop pad after every use and let it air dry completely — or toss it in the laundry. Rinse the water tank and let it dry with the lid off. If the smell lingers, wipe down the pad attachment area and the tank with white vinegar or a diluted bleach solution (check your manual first). Run a cleaning cycle with just vinegar water to flush the system. Then let everything dry fully before the next use.

Future you just needs one habit: take the pad off and let it breathe.