We temporarily moved some CNAME records in our DNS to point to a different server while undertaking maintenance work - we do this every six months or so - and we allow a decent amount of time to allow for propagation.
Everything seemed fine - users were being sent to the correct server, and when I used nslookup to test our primary and secondary DNS, the CNAME data was correct for all the domains we were redirecting. However, when using the service at whatsmydns.com, we were being told by each DNS the service polled that there was an "error: token mismatch" from all servers.
Now that the maintenance work has been completed, the CNAME records have been returned to their original values - nslookup and whatsmydns.com all return these expected values.
I've tried searching for "error: token mismatch" - but all I can find are product/service support forums where the response is simply "your website seem fine", and don't actually identify or discuss what a token mismatch is in terms of DNS resolution.
So - what is an "error: token mismatch" in this context?