You can work around this issue by doing the following:
Configure the application to force an expiration date manually:
1. Go to "Tools | Options", then to "SharePoint" tab, then click on "Settings" button, finally set the following options.
2. Check "Force cookies to expire 19 minutes after they are acquired" (we were told cookies expire every 20 minutes).
3. Set the option "Refresh cookies 1 minutes before they are due to expire".
Try the migration again and it should be successful this time.
This has now been fixed in hotfix build 18.104.22.1681. Please contact support to obtain a copy of this hotfix.