Hmmmm. What if you made a dog-safe, low-fat topper for his food? If you used skinless chicken breast...bones are good for the boiling part, then removed later, added carrots, and some water, then cooked it slowly for a while, you'd have something safe and tasty to use for now, until you get the other food. Just leave out the onion, and it will be pup safe!
Refrigerate it until it's really cold, so that you can pull any little bits of fat off of the top that solidify there, so that there won't be an issue if Thumper gets it.
The chicken meat from the pot, and the carrots, can be cut into small pieces, and fed to them, too, if you like. It would probably be too much, so you can freeze small amounts in Ziplocs.
In fact, you can make a week to a month's worth of the broth, too. Just freeze in ice cube trays, and once frozen, transfer to bags.
Even if we suspect that we know why, it's always stressful when a pet doesn't eat well. Hopefully, a food change will 'fix' the problem.
Love All Life, Thank You For Posting! :)