Depending on which brand of dry food you use, many of them make an equivalent soft (can) food that you could use as a topper and wouldn’t upset their stomach.
I add a can of canned dog food and a can of water and mix it all really well. My old shorthair that has never ate generally will eat most of it. His pup has no issues eating and will eat until anything is gone whether it tastes good or not...
My GWP has the same issues. My personal opinion is that it comes from exhaustion as I notice she eats less and less the deeper into the trip and hunting miles start to stack up. I will mix in some broth or sometimes a pouch of some baby food. It helps but isn't 100%.