Default Rooted with CF-Autoroot, now encryption not possible anymore

I just rooted a brand new Galaxy S4 on i9505xxuemke
Before I encrypted and decrypted several times. Always worked great. Now after root when it should encrypt display shows shortly the green android and then it goes black. Device does not react anymore. After about 1 minute it vibrates and reboots. However I don't have to enter my password to boot. Only to unlock. Now I can go to options and try encrpyting again. Hower same behaviour as before. Any suggestions?
There are no apps installed, no google account and so on. Its factory fresh. I even restored factory settings. Same behaviour.

Any ideas?