S6 intermittent start issue..

Anyone have and idea where I start on this? Camshaft sensor?

One month after car was put on the road it would not start on 20 occasions over an extended period.
Every time it happened when the engine was cold or had not run for a long time. Multiple hours.
Crank but not start. Pushed it to clutch start; but that didn’t work.

Once the car started and ran the problem did not reoccur.

Problem stopped for a period of time. 2-3 months maybe I did not have another occurrence.

Then it came back and would not start at all. If you tried 20 times it might start 1.

Most of the time when the car would not start it took a prolonged period of waiting for it to
start.

On a couple of occasions it would start after a short wait of maybe 20 minutes to 1/2 hour.