1/4" usb board underlayment in bathrooms
First of all, get rid of absolutely all mold and fix those leaks that caused the mold.
Next, OSB is not a good underlayment for damp locations. It swells and wicks moisture. I suggest you tear it out and use a good plywood specifically suited for use as underlay. Regular plywood has voids within the layers that can crush under the weight of a heel. Any good lumberyard should be able to provide the right material.
Lastly, make sure the underlay is secure and smooth. Vinyl doesn't hide flaws, it magnifys them.