The post you've linked doesn't say that it was some unknown/random reason just the fact that the person is locked out of the account, not that the account itself is locked, which may be for variety of reasons(losing 2FA, forgetting password, else?). It's more about that support is slow. The person reached out and the issue was eventually resolved.

> The post you've linked doesn't say that it was some unknown/random reason just the fact that the person is locked out of the account, (...)

Fair enough. You can google though. There's a wealth of complains of people seeing their accounts locked.

If you don't have time to run a Google search, you are free to read ProtonMail's own docs, specially how they describe how they lock accounts based on heuristics and how they recognize the occurrence of false positives.

https://proton.me/support/account-disabled

Thanks for posting this, honestly I was unaware this had been happening as widely to others. Wild.