Galaxy S5 on O2 - Locked out after reset

[Timewarp]

I factory reset my stock S5 using the recovery menu to try and fix battery drain issues after upgrading to Marshmallow, however after reset it asked me to enter my Samsung account details due to "Abnormal factory reset" to prove I was the device owner.

After entering the correct details, it then gives me the message "Processing failed" and won't continue.

My account details are definitely correct (changing the password by one character gives a different message), and I've never logged into the phone using any other Samsung account. I've had the phone since new.

Is there any way to regain entry? I can log into the Samsung portal on my computer.

 

[*Detection*]

Flash a stock KitKat ROM and try logging in again, if it still fails, you'll need to factory reset from recovery (Still with Kitkat) and then upgrade back to MM

Next time, disable "Reactivation lock" before resetting the phone

 

[Timewarp]

Would that invalidate my warranty?

 

[*Detection*]

No, flashing stock ROMs doesn't invalidate it, only if you flash custom (Warranty is determined in some regions by the KNOX flag, if KNOX is 0x0, warranty is valid, if it is tripped to 0x1, it is invalid) flashing stock ROMs leaves it valid with 0x0

 

[Timewarp]

Last ROM I had that was working was Lollipop. Should I try that, or do you still recommend KitKat?

 

[*Detection*]

Has to be KitKat, the exploit was patched in Lollipop, best to go for an early build, pre-June 2014, basically just choose the first one available from sammobile .com or wherever you download them from

 

[Timewarp]

Exploit? Will logging in directly work on KitKat then - or do I have to do some workaround?

 

[*Detection*]

I've told you how to do it, read some threads, that's how you fix it when you mess up by leaving reactivation lock enabled

 

[Timewarp]

And I really appreciate it. Thanks!