I had exact same problem, car handles great through big puddles but doesn't swim too well!
Driving back from Bristol to Bournemouth on a wet night, hitting all the puddles (couldn't avoid them). Hit a mahoosive one, side skirt popped off at front (no damage fortunately), and then engine cut out. Left it for a while and started fine. A tiny drop of water in mad sensor, so dried it all out and reset the Ecu light.
Sorry it doesn't answer your question, but thought I would share anyway
You can't win the lottery without a ticket!