Flashing TWRP; stuck on 'Sony' logo?

After unlocking my Sony Xperia Z Ultra using the official Sony guide, I connected it to my Windows 10 PC with the intentions of flashing the latest TWRP 'img' file (as of 12/09/15) to it, I did so and rebooted. After the reboot, the phone didn't boot into the recovery but instead into the normal OS. I turned the phone off and tried to flash the latest CyanogenMod nightly (as of 12/09/15) and attempted to boot the phone normally. The phone was at this point stuck on the 'Sony' logo. Any solutions or suggestions?

Thanks in advanced!

(PS. I tried to boot into fastboot and re-flash CM12.1 but I got the 'FAILED <remote:command not allowed>' error. I can still access fastboot and flashmode and yes am 100% certain that the bootloader is unlocked.)