Please help

My girlfriend has had her dog since he was a pup and never got him trained too well. He’s been a crate dog, and since living with me i’ve paid for dog training sessions weekly over the last few months. He’s typically a very hyper but submissive dog, but never aggressive. He never barks or growls at people. The training has helped us learn how to teach him commands, and get him to listen to commands better, but for some reason he is becoming more aggressive when seeing people or animals on walks (he used to ignore them), the more we train him. It’s like the submissive side of him is going away and becoming more aggressive in turn. Our trainer says we need to do more with him, but we are doing more than he’s ever done before and it’s only making it worse. I’ve read the wiki, i’ve spoken with the trainer, and i’ve looked up other answers as well, but nothing seems to fix or explain why his behavior is becoming worse when his living arrangements are becoming better. He’s less fearful than ever, which makes us think him being afraid kept the aggressiveness in check but that is NOT what we want or ever went to go back too.