I'm sorry for the inconvenience. This sounds like a bug but I cannot reproduce it and you're the only person reporting it. It's supposed to display the announcement only once the extension updated to the version 1.22.x. The announcement has been removed in the new version anyway.
BTW, you're supposed to contact me or post an issue here https://github.com/gildas-lormeau/SingleFile/issues when you encounter a bug. The advantage is that this "trick" works for any open-source project. It's more productive because your comment has been flagged as a "bug report", it will surely be deleted and will have served absolutely no purpose.