It might have flared up again as a result of being moved. It can sometimes take several weeks for them get over a stressful event such as being moved or re-housed with new tankmates.
When I first added my Rustys, they always hid on me approaching the tank, I had one with a slight scrap down its side, took it out and treated with Melafix, seemed to be all clear..put it back into the main tank and it scrapped again.
It is weird though it is happening over and over again..my suspicion and this is only a suspicion is the Male Kenyi being overly aggressive...a lot of aggression goes un-noticed by us and it is possible it might be that.
I would keep the treatment going for a week after it is showing signs of recovering and leave it in the hospital tank for a week after that as well...if once it goes back into the main tank it develops it again, then there is something going on which needs to be sorted somewhere.
Best I can really offer..