I’d discuss the situation with your vet. Though none of my rabbits have ever had ringworm, I have had mice get ringworm, and it isn’t always that obvious or clear. The symptoms can be atypical.
About you, as medications are used year after year, they often become less effective because the microbes they are killing evolve a resistance to them. You hear about it a lot with antibiotics, but it’s been happening with other things too. Head lice have become extremely resistant to most pesticide shampoos.
Older remedies often work much better than the chemicals the microbes have become resistant to. I have an old fashioned athletes foot remedy that has always worked well and is totally harmless. I’ve never tried it on ringworm, but they are both fungal infections, so I figure it can’t hurt to give it a go. A long soak in salt and vinegar. I wouldn’t do it as a substitute for conventional treatment, but since the conventional treatment is failing, maybe give it a try along side the conventional treatment.