https://www.cnet.com/news/twitter-removes-locked-accounts-from-follower-counts/

Locked accounts are those that Twitter has locked the owner out of, either temporarily or permanently, for reasons such as suspect behavior that indicates the account might have been compromised.

In a blog post, Vijaya Gadde (‎@vijaya‎), Twitter's legal, policy and trust and safety lead, explained, "In most cases, these accounts were created by real people but we cannot confirm that the original person who opened the account still has control and access to it." This update goes to bolster "account credibility" since follower counts are public but the other metrics aren't.