I discovered after a few days in Mammoth that many of the photos I took using Camera FV-5 (version 3.31.4) on my Samsung Galaxy S7 (SMG930F model) were jpeg only, no DNG file was saved. After a little experimentation I discovered the problem and a workaround. It turns out that when I start Camera FV-5 it saves DNG as it is supposed to do. However, if I leave the application in any way (open up a browser, press the right button to lock the phone, etc.) when I return FV-5 now forgets to save a DNG. I don't know if this is a bug others would run into or specific to my phone. I reported the bug to the developer.
Workaround: Always close and restart Camera FV-5 if you switch away from the application. When I do that, I get DNG saved 100% of the time.