I would do a gratin casserole withpasta . Layer of cooked pasta then sauted garlic with the chicken shreds, a layer of white sauce ( usually bachamel)then a layer of cooked pasta, a layer of sauce again and top with mozzerlla cheese. Use some nutmeg ,black pepper for the sauce.
I hope this helps.
HI since as you said you have been using the same recipe for years and didn't change it , I would suspect the problem has to do with the ingredients , chech te expiration date of you baking powder for example.