All four servers: SR2, SR3, Jasmine, and Kobold have been migrated to their respective target servers.
As far as those that had MX entries disappear - the cause in every case so far is that the domain was set to 'LOCAL' or 'AUTO (Local)' via cPanel -> MX Entry.
In short people are editing their DNS zone and updating MX records or doing it via the MX Tool and not setting it to 'remote' when using remote mail.
We've written a script to check for this and correct it but unfortunately we can't go back into the past and fix it. Moving forward it shouldn't happen again.
This has affected a small portion of our customers - but I am sorry for those that it has affected.
Open a ticket if you're having issues and we'll address your issues as quickly as possible.