All of my generators around the house are propane. As are some of my shop heaters. I bought all of my tanks (5) new and they all have different sensitivity when turning on the tanks. Some of the tanks I can open with a normal turn of the valve and others, like the 30 on the 4Kw generator, are super sensitive and need to be opened very slowly. The 30 you can actually hear the OPD click if you open it to fast. Before throwing any money at this "issue" slow down your valve opening speed and listen. You just may hear the OPD click when opening your tank. If so, close the tank valve and reopen it slower.
You said that the propane devices work for a while and then stop. This is most likely due to the propane in the trailer lines from the previous use and then the OPD check ball hitting the seat when you reopen the tank does not allow any more propane flow out of the tank.
Randy