Many users get shocked when their Twitter blue checkmark (verification badge) is suddenly removed. Sometimes they think it’s a bug, but most of the time it’s not. Twitter can remove verification for many reasons. First, if you change your username or profile picture often, their system might remove the badge.
Second, if you break Twitter rules like spreading fake news, abusive tweets, spam, etc. they can take it back. Third, if you stop being active for a long time, Twitter may also remove it.
Recently,
Twitter also made verification a paid service (Twitter Blue). So if you don’t pay or cancel the subscription, you lose it. Some people also face technical glitches, but that’s rare. If you suddenly lost your badge, check your email, sometimes Twitter sends a reason. If not, then check if your subscription is still valid or if your account broke some rules. If you believe it’s a bug, you can raise a ticket to Twitter support, but honestly they don’t reply fast. So, mostly it’s about rules or subscription, not really a bug.