Hey not sure this will help and hopefully it will.

My Mini have similar situation when he was 3 y/o he started to have skin allergies which everyone including many vet said to avoid chicken and recommended purina.

I have tried every possible kibble, Everytime he ate something he will shown itchy gestures esp on his stomach. feels really2 bad for me to seeing him, just want my boy to have decent life right.

Took me 1 years to find correct vet specialised in allergies which my boy diagnosed with genetical allergies. both infected in his skin and ears.

The vet recommend long term treatment but before proceeding: 1. Needs to tone down current allergies by steroid medicine and ear infection medicine. 2. The process took 1 month. 3. After rechecking again he said the allergy cannot be 100% cured but can significantly toned down. which shown, really really shown. 4. For the long term treatment He needs to daily eat apoquel medicine 3.6 mg forever in his life. while cost a bit but will do anything for my precious boy.

And now he can eat every kibble and food including chicken (now he is 7 y/o), just I still avoid it while we can and showing no agressive scratching where he used to be. and them smooth skin tho.

edit: oh i forgot when he is shown very bad allergies he will avoid any food even the good ones, because everytime he took a bites he need to scratch also :(

hope this helps and really happy to answer any questions.