I had this issue when not setting a password on the wallet.
It wouldnt take my pin - all though id get a success key[0] toast notification and it would bomb me out.
After checking through the phones files I found /data/data/puki.blockchain
In there was a GUID - which was the identifier.
After trawling the source code I found that if no password set the default is:
If you set no password on your account and just a pin by default the password is:
PIN + PIN + PIN
That's not to say 3003 + 3003 + 3003 = 9009.
Go to the website. Enter in your identifiyer.
For your password (pin in this example is 3003) enter in:
300330033003
and your in! Just worked for me. Blockchain support are useless.