Dog collapse

My dog is about 1.5 years old, male, neutered. Breed is mixed but mostly American Pit Bull Terrier and American Staffordshire Terrier (DNA test confirmed). He was born in an animal control facility and transferred to my county's Humane Society, where I adopted him from. He had some skin issues when I got him that resolved with a stable, quality diet.

A few months ago, he was playing outside with my friend's German Shepherd, running and wrestling, and he collapsed. He tried to get up but it was as if his legs couldn't support his weight. It was on the warmer side so I assumed it was just heat sickness, and I carried him inside, gave him a few sips of water, and put a fan on him, and continued to give him tiny amounts of water. He recovered quickly and was back to normal by the next day.

Then a few weeks ago it happened again, exactly as the first time, but it wasn't anywhere close to hot that time.

I took him to my vet, who suggested it was either neurological or cardiac. I have seen seizures in dogs before and am pretty confident that wasn't the issue, so she referred me to a cardiologist. I've got him set with an appointment there, but while I was going over everything with the cardiology clinic, they suggested it didn't sound like a heart issue given the time lapse between the two events, and recommended I read about exercise-induced collapse and see about testing him for that.

I did do some reading on EIC and nothing I found even hints that it's been seen in pit bulls. I still plan on getting him tested for it, but I am just looking for any other potential causes that I can try to pursue with his care team.