Norcold fridge trouble shooting

I have a 2007 Norcold model 611 refrigerator that when plugged into the shoreline, the freezer and fridge both work (Refrigerator works just average)

but…

when running off of propane, only the freezer works while the fridge does not cool down or work. 
Anybody have any troubleshooting ideas; I’m pretty good at U-tubing things and fixing things on my own, but I don’t know where to even start????
(I’ve cleaned  the burner and the flame is great. )

Appreciate your help and thank you 🙏