I use Speedplay Zeros and have gone over twice.

First time was back in the spring, about 120 miles into a 140-mile ride. Unclipped left at a traffic light... put my left foot down and slooooooowly shifted my weight to the right. Started tipping & fell over on a couple other riders stopped at the light. Slowest fall ever.

Other time was a couple days ago - second time riding rollers. Drifted left, things got sketchy and I was down in a flash, to the left (only had potential support on my right).

Can't blame the pedals or cleats - it was user error both times.