Same problem here. I also have the V6 ( Xbox360E 4GB toshiba nand. MFR Date: 2013-11-4 )
I can reliably get it glitched to Xell without any problem, but as soon as I flashed the hacked nand, the Xbox just won't glitch at all, not even the Xell anymore. I have tried all the software that I can find to build the hacked nand.
I have to flash the original nand back first, then flash the ecc image, to be able to get it glitched in Xell again.
I think there is something not compatible with this V6 in Xebuild. Hope the issue will be looked at soon.