I had the same problem a couple of years ago while visiting my brother in Breckenridge Colorado. The fridge wouldn't light and I was getting explosion noises from the burner assembly when it was trying to ignite. I contacted Dometic about the problem and their response was "We never heard about this type of problem; take it to an RV repair shop to be fixed - it's broken".
The fridge worked fine at lower altitudes so I decided to disassemble the shielding on the burner unit to see what was happening. Once the covers were off, the problem was obvious. Dometic has a 1" air gap between the gas jet and the mixing pipe leading to the burner assembly. While looking at this, I realized that it looked very much like the burner assembly on my gas grill but the gas grill, which burns much more gas than the fridge, had an adjustable opening to control the gas/air mixture. At tihs point, I realized what the problem was. At low altitudes, air pressure keeps the propane jet confined enough to properly enter the mixing tube while at 10k' altitude, the propane was spreading out so much that most of it was going around the tube into the combustion chamber. When the gas concentration reached a critical ratio, it exploded when lit by the igniter.
My solution was to make a shield that fits between the gas orifice and the burner tube. The shield is about 60% of a tube and is attached to the existing sheet metal using a screw that was already in the right place. This completely solved the problem. I also checked the burner after it was lit and verified that the flame was still a nice pale blue color.
The minute amount of propane that's burned by the fridge doesn't require that full 1" air gap. I've rechecked the burner assembly at low altitudes and it still looks good so I left the shield in place so I don't have problems at high altitudes again.