That’s a shame, Chris. While disease in Chaffinches and Greenfinches has been much publicised, Bullfinches and other species can suffer. An interesting article can be found at https://www.gardenwildlifehealth.org/portfolio/leg-abnormalities-in-finches/.
If it’s a lot of birds affected, it might be sensible to halt feeding for a while. Otherwise ensure cleanliness at feeding stations.
I have had Bullfinches visiting our feeders for the last few years with no problems but recently i have had X2 poorly males One has died! whether to an illness or to a local cat ! I clean my feeders & area regularly we have a good number of greenfinches with no problems ! has anyone heard of any problems?? and do I stop feeding??