Twice I have had to have the propane lies cleaned out on our camper because mud daubers plugged up the lines.
Mud Daubers seem particularly fond of the smell of propane. "If" they can get into it they'll build their nests on the furnace or the refrigerator LP orifice. One of the easiest places they like to build nests is on the propane orifice of the hot water heater. If you experience problems with any of your propane appliances check for mud nests. The same holds true with spiders. They also like the odor of propane. Or let's say the odor put into propane so we humans can smell it.
I also saw this on another site "It sounds as though your regulator diaphragm is clogged up and therefore not able to vent properly. This is commonly caused by the regulator vent being blocked by a wasp or mud dauber nest. The vent should be located near the bottom or side of the regulator near the LP tank(s). It typically has some mesh or a screen over it to keep debris and bugs out. However, oftentimes wasps and mud daubers, whom are attracted to LP odor, will build nests on them"
Hope this might help.