Stop start didn't start (properly)

So, our '14 Superb 170CR DSG did a weird stop-start thing today. We were in a very long queue of traffic (maybe 20mins) and it happened to be a hottish day today (guess 25C). Everything was working just fine with the engine stopping and starting exactly as it should when.....

The next time it comes to start, the starter cranks the engine at the usual speed and we hear it catching but then it died immediately - almost like a cough. It did this two or three times in a row before we decided to engage park and turn the car off. After that it started just fine.

We decided to turn off the stop-start until we parked up maybe 5-10mins later. Everything was working just fine on the way home.

Any ideas?