Problems with a dog at training

Just recently my bully boy seems to have real problems with one particular dog at training a male husky both have been done. We attended two separate classes and have no problems with the second class which is outdoors also attended by two huskies but my bully isn’t bothered by them at all. My bully becomes aggressive which he never is, he is normally a laid back guy who loves all dogs. I’m not sure if the fact that the huskies sister also attends the class has anything to do with it. I am at a complete loss and I am getting really down about it now.