Passenger airbag doesn't turn on sometimes

We've had the truck for two whole weeks now and we've noticed that the passenger airbag will, on rare occasions, show off instead of on when my wife is there. If we stop, kill the engine, and she unbuckles and gets out, then gets in, rebuckles, and I restart the engine, it shows to be on. We usually start the engine before buckling in, Texas summers heat up the inside of a car quickly and I don't waste time getting the cooling started. Is this something I need to have checked, or am I causing this during the buckle/startup sequence?

 

The sequence doesn't matter if the transmission is in park tho it can be in drive and it should still pick up someone getting in the seat.

Sometimes it may kick out depends how she sits in the seat like the edge for example.

If none the above solve the problem take it to the dealer and have them test the weight sensor in the seat.