Once on the MUP I came on a fully-kitted road rider at the side of the path staring at her flat tire. Wife and I stopped, and my wife asked her to let me take a look. The tire was about 23 mm (narrow racing clincher rims) and tubeless and the tire was totally separated from the rim. She had just taken delivery of the bike and was out on her first ride. There was no clear sign a puncture or outer surface damage or otherwise of how it started. The sealant was gooey all over the outside of the tire. I tried to realign the tire edges inside the beads and get some air it it, but it didn't work and we were out of options - she had to walk back to her car. I assume that for some reason, perhaps a bump, the bead separated and there was sudden deflation. Tire traction then pulled the beads loose completely.
Just an idea. Can a tubeless bead be knocked out of engagement by riding over a bump with insufficient tire pressure? Is there some kind of bead adhesive that could have helped keep the air in?