I'm not a banking expert, but I can give you some "common sense" answers.

Is it possible you've been mailing your check to the wrong place? One possible explanation is that the wrong government office, or a private business, or a person, has been receiving your check. They deposit it in their own account, and then later, when the error is discovered, they reverse the transaction and the money reappears in your account. This may sound scandalous, but it is really quite a common occurrence.

By law, businesses are not allowed to keep money that is paid to them by mistake, but as long as they return the money within a reasonable time, they are not deemed to have done anything wrong. So if a business receives a check and they don't know what it's for, the rule of thumb seems to be: when in doubt, deposit the check first and ask questions later.

The fact that the "payee" named on the check doesn't match the owner of the account is not an obstacle!

When you mail your check, are you enclosing the proper documentation to show what the check is for? If they can't match it to your account, they will probably reverse the transaction, as above.