Hi @Joan_JG - welcome! And sorry to hear that the vault isn’t locking the way you might expect.
Some have encountered unexpected behaviour with a recent update to the Bitwarden extension on Chrome that was released a couple of days ago. The good news, is that it looks like everything is back to normal with the latest release (version 1.56.4). I expect it should be available to you very soon if you check your extension update status.