Some cases of bumblefoot can be so stubborn it can require months of treatment. I have such a hen.
She came to me with one of the worst cases of bumblefoot I'd ever encountered. Both feet were affected, one so bad, the foot was twice the size of the other. Her previous owner had never thought to give his flock foot inspections, and she had been living with bumblefoot for years most probably.
I had heard that stubborn cases require repeated soakings and continued treatment, but as her infection returned, black scabs being the evidence, I was reluctant to operate and cause her further pain. Finally, I had to intervene and again she went under the knife.
I'm doing every other day soaks, and cleaning the wound and re-bandaging in between. Her pad remains very swollen but the black scab has yet to return, which I take as an encouraging sign.
My advice is to persevere and keep treating for as long as is needed, even if it requires months of care.