Couple thoughts I have...
-Are you using cheesecloth?
-Are you using cloth towels during your make - either on your hands or anywhere else in the process?
One way that you can spread yeast infection is through using cloth that has been used, or machine washed with, items that have been used in every-day operations around the kitchen/home.
When using cloth items in cheesemaking, it is best to start out with new towels/cloths and dedicate them only for your cheesemaking and no other use. Don’t wash them together with any other items from your household (wash separately), and when done washing/drying, you can set them aside with your other equipment, perhaps in a zip-lock bag, to be used only for cheesemaking.
For myself, I decided that I was only going to use paper toweling rather than cloth towels while making cheese. I do use cheesecloth, however, and do wash and re-use it. I just do them separately from any other wash. I rinse first in cold water, then wash them hot, occasionally using a little bleach. Just need to be sure the bleach is all rinsed out!!!
Not sure if any of that applies but thought I’d put it out there just in case it could be helpful.
Sue - AKA ~Leah’s Mom~