It takes a long time to export and you've seen it fail.
The export used to work before you imported thousands of roles into the environment...
IMPORTANT: This article contains information about modifying the registry.
Before you modify the registry, make sure to create a back up of the registry and ensure that you understand how to restore the registry if a problem may occur.
For more information about how to back up, restore, and edit the registry, please review the relevant Microsoft Knowledge Base articles on support.microsoft.com
Perhaps your IE is timing out.
Try changing the following registry entries, as per Microsoft Site:
KeepAliveTimeout DWORD value 99999999 (in milliseconds)
ServerInfoTimeout DWORD value 99999999 (in milliseconds)
Release: CAPUEL99000-12.5-Identity Manager-Blended upgrade to Identity &-Access Mgmt Ente