I have processed thousands of sheets of film over 35 years and that includes the last couple of years 4x5 Acros and I have never seen this problem before. Actually it looks like a platinum print made on an unevenly humidified piece of paper. My guess is this is a factory defect. I would expect Fuji to have very high standards and very tight quality control but stuff happens. I once got a bad batch of film from Ilford so it can happen to anyone. That is my vote, especially considering all the films and developers you have done and not seen the problem. I hope it goes away for you. You might open another box and try some out of it.
Dennis