I've heard that prong collars can increase aggression sometimes. The dog is excited to see the other dog so they pull, they receive the pinch from the collar from pulling, then associate the pain with the other dog, which could cause them to react badly to meeting a new dog next time. I've used prong collars before and I thought that Nebo seemed to react worse to meeting new dogs while wearing the prong collar. (My dogs are pretty good with other dogs when meeting them off leash but they can all be brats when meeting on leash especially if I have multiple dogs.) I'm not saying this will be the case for you but something you might want to look into.

A random side note on the hackles...Keva and Skya are so weird. If they haven't seen each other for a while (like I took one to work) they both react with huge hackles up and growling when they see each other, never a fight, they just get their hackles up and growl then run off to play together totally fine. Strange dogs.