Why did I get a VAC ban when I wasn’t even cheating?

I was playing normally, recording gameplay like I always do, when the match suddenly crashed and Steam showed a message saying VAC couldn’t verify my game session. The next day, my account was VAC banned — same thing happened to a couple of my friends. I’ve never used cheats or third-party tools, and my account has over 8,000 legit hours. It feels really unfair to get hit with a permanent ban for what looks like a VAC system error, and there’s no way to appeal it either.