As per Microsoft those who are in the Windows Phone 8.1 Developer Preview will need to downgrade to 8.0 prior to installing the Windows Phone 8.1 + Cyan update (when it becomes available).
Microsoft knows it's known issue and doesn't know when a fix will become available for those in the Developer Preview program.
"We are currently investigating the issue. We have paused delivery of the update to customers using the Preview for Developers, and will resume once a fix is in place. Customers whose phones have been affected should use the Nokia Software Recovery Tool to return your Lumia to a normal commercial software state before downloading the Lumia Cyan update. More information about the tool can be found at www.nokia.com/support/recovery-tool."