We used to show a special error message when we got this error; however https://github.com/matrix-org/matrix-react-sdk/pull/783 made that not work. You'll only hit it if you're upgrading from some ancient version of Olm, and I'm quite happy for us to fall back to the generic 'couldn't restore: vape your storage?' flow in that case. (In any case that's preferable to dumping you at the login prompt with no warning that we've just vaped your storage).