That being said, there are several factors.

What is the ambient temperature?

Is the sun shining on the wall where the refrigerator is located?

Have you checked and cleaned the burner and orifice?

Is the flame audible? There should be enough propane flowing that you can hear the flame when standing beside the lower vent. If it is quiet, then it is possible that the orifice is partly plugged or there is an oily residue build-up in the propane lines.

Do other propane operated appliances have a good flame? Even if they do, the lower gas flow for the refrigerator still might mean that the line needs to be blown out.

To blow out, shut off the gas. Disconnect the line at the refrigerator and the regulator. Place the end of the line from the regulator in a bucket or something similar. Use air pressure to blow out the line from the refrigerator end. If the oily gunk is the problem, you will see it in the bucket. Reconnect the lines after cleaning the burner and orifice (don't poke anything in the orifice opening. Just use rubbing or denatured alcohol). Turn on the gas and test the connections for leaks. Purge the lines by turning on the stove until it lights and burns steadily. Then try to turn on the refrigerator. It may take a number of attempts to purge the branch leading to the refrigerator before it finally lights and stays lit.

Let it run and check to see if this fixed the problem.