I raised a bug against Cloudflare in the morning and they are checking the issue. They believe it might be due to SPDY but not sure as SPDY is being used in all browser Chrome, Firefox, IE to speedup caching.
en.wikipedia.org/wiki/SPDY
Thanks for the update. I tested the user registration workflow number of times by enabling/disabling cloudflare. User creation failed in all the enabled instances even after purging cache from cloudflare and reducing down the cache setting to basic. I tried from android and the default IE browser from andriod too having same issue. Firefox had no issues.
I hope they will come up with solution. In case they pointed something related to CB I will let you know.
thanks
amit