For the weight loss, please go to your vet for a full blood panel test as reduced nutrients could lead to other issues.
Second, do this test for allergic triggers in food and environment: https://glacierpeakholistics.com/collections/frontpage/products/pet-wellness-life-stress-scan-1?variant=38717885892
Third, no more potatoes, of any kind, any color, in any thing. Very bad ingredient used by many as a filler in dog foods. Causes harmful gas and bloat.
Look into the Zignature line of dry, limited ingredient kibble. Many to choose from. Over feed. Rather your pet eat enough and leave some in the bowl, then underfed since you don’t know which meats his allergic to.
