This reminds me of "ice mode" in BMW E36 M3s. In rare, very rare cases, the ABS would think it was on ice, and braking would all but disappear. I had this happen twice on a race track, and gong into a 40 mph corner at 100 mph is far more excitement than I like.
It was not repeatable, it appeared to be a combination of vehicle loading and quickness of brake application. Unload a tire or two just right, hit the brakes hard, and voila!! No brakes! To get the BMW bakes back, you had to let off of them entirely, and they would normally return. But obviously, your lap time was shot at that point!! :frusty: Luckily for me, I somehow recognized the issue and let off the brakes and got back on them to keep it on the track.
Due to the randomness and number of folks it has happened to, it sounds similar. A very specific set of circumstances line up just so, brakes applied in just the right manner, and voila, no brakes. But no obvious failure. Also, extremely difficult to diagnose.