I had never heard of this until I was watching Dr Pol the other day! His son's hen had scale mites, it looked awful, but was treated easily so that's a good thing.
A photo of your roo's feet would be more helpful in answering your problem...hard to know what it might be without seeing it.
I had a hen many years ago who lost a toe, suddenly and without any indication of what happened. I was watching the girls get up to roost one night (webcam in the coop) and noticed there was blood all over the place! Ran outside to see if everyone was okay and found my PBR sitting in a pool of fresh blood. Brought her in, cleaned her up, and discovered the nail and toe to the first knuckle were just gone! Several peroxide soaks and a night in the cat carrier in the warm laundry room and she was good to go back out the next day (only because I didn't have anywhere inside for her to hang out). It was the strangest thing though...we had been sitting watching the camera as they went about their evening routine and then it suddenly looked like a murder scene. We didn't have any predators that could get in...so out best guess is that there was a squabble getting in the coop to rest and she either got it bit off by another hen or caught it on something and ripped it off herself, but it was a very clean wound, so neither was very likely. It was the one and only injury other than my hens dying of old age that we experienced. This time around, we have raccoons in the neighborhood now.