Hi our female Joey gets it sometimes, I've notices it happens if her feet are not dry, like after a rainy period or if she needs to bath often. I have heard it can also be the food, but that I have no experience of
I treat it with epsom salt and it works really really great for us. I put quite a lot of epsom salt in a small bowl with some lukewarm water. Then I try to hold her foot in it for as long as I can, it mostly only works for a minute or two cos she gets tired of it. Then I dry her foot real well and the cyst is usually gone or at least much better the following day.
Hope this works for you too if it's not getting any better maybe it's the food? I'm sure someone else will come along that know more about the food thingy