Very interesting. Before you changed your email address, are you sure that your vault login items were present but blank (as you showed above), or is it possible that the entire vault appeared to be empty with no login items to list (as shown here)?
Also, do you by any chance recall having either changed your master password or used the “rotate account encryption key” option around the same timeframe that you changed your email address?
FYI, there is a (usually fairly benign) sync issue that happens from time to time, in which the vault appears to be completely empty after logging in — this can be fixed by logging out and logging back in.
However, by changing your email address while the Web Vault was in such a state, you may have triggered a corruption event similar to the bug that @Quexten has demonstrated in GitHub Issue #7709. @Quexten, what do you think — is it possible that the email address change by itself (with no account key rotation) could have a similar end result?