My Discovery 5 does exactly this as well.
Dealer can't find any problem. I have been reporting it for years, ever since I had the car. In my case, the problem happens only every now and again. Regardless of engine speed, traction slowly comes back and all is normal. No clucking, just smooth return of connection after a few seconds. Feels like low oil levels but, like you, they are normal. My latest suspicion is slow electronics. My Nav system sometimes takes up to a minute to boot up correctly. Dunno. I'll report back if I can diagnose it. Cheers.