I don't think a warning was necessary. The drivers all know it's against the rules. The safety car was having trouble staying on track in some of the corners so it wasn't a great time to play games with Max. I would say that probably contributed to him getting a 10 second penalty.
No car may be driven unnecessarily slowly, erratically or in a manner which could be deemed potentially dangerous to other drivers or any other person at any time whilst the safety car is deployed.
They had the telemetry from his car, so they had a good idea if it was enough to be considered erratic. He also did the same thing on an earlier restart.
It wouldn't shock me. He just needs a decent car to be in contention. It's pretty clear based on Laswson and Yuki's results that the Red Bull is in the bottom 3rd this year and the points finishes he gets are all because he's just that good.
I've been doing them on the recteq lately and they have turned out great and are so damn easy. I usually do st louis ribs, so I've cut the time back because they don't need as long as spare ribs. I give them 30 minutes on 250 and then turn it up to 275 for the rest of the cook.