I instantly thought Mereks, GFF vacinates though. The females that past were never thriving 100%. I know not all birds can be perfect & just assumed they were not ment to make it. However the male was always perfect until last night. He is in a large wire dog crate away from others with medicated water & he is drinking it. It's so hard when there are no other symptoms. I am watching closely for anything to give more clues. If he doesn't rebound neocropsy is at the top of my list. If he has something that puts my flock at risk I would be sick! My rhodebars have never been near any other birds thankfully.
The Marek's vaccine does not create immunity, merely inhibits the growth of the tumors. Birds can still be infected, become carriers, and die from the disease even if vaccinated.