Any chance you just put in a new tank? Every once in a while, I get a tank where I need to screw on the regulator super tight so that the propane flows right. Maybe try tighten it?
I've also seen on some grills where you have to have the knobs turned off before you open the tank valve. I think that usually just limits the gas flow, won't cut it off, so probably not your problem.
There is a safety feature built into the regulator, if the grill is lacking in temp, turn off all burners and gas bottle. Turn gas bottle wide open and then turn on one burner and light. This resets the regulator, if a burner is left on when bottle is turned on regulator limits psi bc it senses a leak.....learned this the hard way lol