On this morning's Tour de Cure, the first flat I fixed was on an e-bike running 700x38C Marathon Pluses. They're beefy beasts. It was surprising that that tire would have flatted. Didn't figure out the cause onsite - nothing in the tire or in the tread, rim & strip were fine, etc. The punctured tube is mixed in with several others needing later patching, so I won't know with 100% certainty which one was inside the Schwalbe, but it'll be interesting to see where the hole is.