Microsoft has issued a statement and recommends users downgrade the Windows Phone 8.1 Preview for Developers to commercial software before downloading the Lumia Cyan update
Here's the full statement from Microsoft:
"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."