If I remember correctly, he noticed that his account with 100,000,000 plus followers was only getting 40,000 or so views. This lead to a Twitter engineer saying maybe his content wasn't interesting enough to get views and getting fired. And later on Musk said that they found a bug in the fanout system because his account was so big it basically broke things and they fixed it.

I remember everyone agreeing with the Twitter engineer who said maybe his content wasn't interesting enough, while to me that seemed odd. If people follow an account and they tweet and they're online they should have a high chance of seeing that tweet. That's the entire point of following someone. If someone I've followed tweets something I would like to see it.