I'm not clear whether you are talking about the regulator at the gas bottle or the regulator that turns the flame down on the BBQ.
I have had problems with the regulator at the gas bottle which had same issues that you describe as well as having reduced heat. There was a fine gauze filter on the inlet to the regulator which had been clogged but I didn't find this out until I'd replace the regulator.
The gas pressure can be easily tested by rigging
a simple manometer from nylon tubing. Double it up and fill with water
to level of 6" or higher. Flick with your finger to get all the air bubbles to come to the top. Connect one end to somewhere on your gas line. Note you will need to turn the BBQ on to get a representative reading. You should get a difference of 11" in your manometer.
Of course follow sensible safety
precautions when dealing with LPG and above all don't attempt testing in an enclosed space.