Birds have to eat. Impacted or not. Greens may move slow, but they won't feed yeasts. It takes a minimum of 5 full days on the Copper to work. Copper Sulfate can sometimes take 7 full days to kill off yeast. I've seen it take 10 days. So a few days is not enough to judge. And yes, many times other internal issues are going on like internal laying, reproductive cancer or Liver disease All these are extremely common in hens, swellings from any of these can close off or slow the emptying of the waste and crop. And of course any disease will lower immune function causing yeast infections all throughout the body.