We had a similar thing happen when our trailer was new. One side worked fine and the other tank didn't. It turned out to be a bad line from the tank to the regulator. The dealer we took the trailer to said they had a run of bad hoses on some travel trailers.
2011 Eagle 330RLTS with just about every option.
Dodge SRW 1 ton Cummins powered.
I was born with nothing and I still have most of it left.