One time I had almost 1 million extra dollars show up in my Waterhouse Brokerage account. I thought, "huh, that's interesting." It disappeared 4 days later.

Yup, it wasn't as much, but I magically had 10k show up after I made a deposit through a bank teller that stayed there for 2 weeks before finally disappearing.

My father withdrew cash from an ATM a while back, he got less than he asked for but had the asked for amount deducted from his account. He complained. The manager of the bank nodded knowingly when he complained. He wasn't believed. He was told that at the end of the month they would do a stocktake and see. Some months later it was credited back. This is about the best of my bad banking stories. The time our deposit for a house got lost was stressful several years of hard hard saving vanished during a transaction.