My Defender Limited did the same thing two rides ago. We were riding in the high desert, where temps were in the 90s. Several miles from the trailer, as I slowed to a stop at a fork in the road, my Defender just quit. It would not restart for 15 minutes, then just fired up and ran normal, until the next stop several miles down the road, where it died again. It did this six times that day, each time requiring 15 minutes cool down before it would restart again.
I took it to the dealer, explaining that I thought it was vapor locking. It had thrown no codes, and no dash lights were on. The dealer did not find any problems with the fuel system, but instead said that with just 600 miles on the machine the clutch was dirty and two washers inside the clutch had worn, so the clutch wasn't disengaging fully, which caused the engine to stall, and the still partially engaged belt would not let the engine restart. They rebuilt the clutch for $345 🙄. The next trip the Defender ran fine, with no problems at all. But the next trip was at 9000 ft elevation and was 25 degrees cooler than the previous trip.
I'm not completely convinced it was a clutch problem, because the clutch had been working fine, and didn't feel like it was hanging up at all. And the Defender wouldn't start, no matter what gear the transmission was in. I guess I'll find out the next trip in warm weather.