After upgrading several WordPress sites a blank screen appeared on a couple of those sites.
One blank screen was using a 'Secret Key' that included printable ASCII characters. When the secret key was changed to include only alpha-numeric characters (a-z, A-Z, 0-9) the problem was resolved.
The other white screen incident was caused by the include folder not fully uploading. When deleting the folders there was a file named '.pureftpd...' that was difficult to remove. Reloading the include folder solved the issue.
Hope that helps someone.