If it was bitter, that's not the PR. Milk was off, or contaminated, or something similar.
Surface PR applications are a way to introduce some more aroma and presentation.... they do very little for flavor and texture. Some PR strains are a little proteolytic, but most are not and work primarily on fat. Plus, the amount of time and conditions for PR to grow for it to break down cheese are challenging to achieve on a surface application.
If you are doing a full lactic blue with openings, that's very much about starter strain selection, milk quality, and most importantly the curd handling. It's easier to do a semi-lactic, gives you more pH flexibility.