I like what NVD said.
I don’t add any acid such as vinegar to my ricotta. I use goat whey that has been made with a mesophyllic culture. (Different than the mozz you are working with.) I just put the whey back into the empty cheese pot after draining the curds, then slowly bring it up to *just* a rolling boil. The curd mass floats to the top when it gets hot and can be drained then for a creamier cheese, but I found that letting it boil just slightly before ladling off the curds makes for a “fluffier” and drier soft cheese that is more like a cream cheese spread in texture and very good. Because of the boiling, the curd mass is in clumps rather than whole, but still floating and just as easy to ladle out.
After doing it this way for a couple of years I wonder why vinegar is ever called for at all. It may help get the last little bit of solids out of the whey, but it adds that sour taste you mentioned. I get whatever curds I am going to get with heating alone and then fertilize the garden with the rest of the whey. I have never had trouble getting a curd once the whey gets hot enough. I am also thinking that the lipase in the whey you were using would have also added its own bit of flavor to the ricotta, perhaps making it less mild tasting.