Question Flashing via recovery reboots phone

Hello there!

I have an international HTC One with ViperOne 5.5.1.
I recently made my phone S-OFF (it has 1.54).

Now the problem: As soon as I try to flash either a kernel or a bootscreen, the phone reboots. I currently have CWM Touch (just 5 minutes now, I flashed CWMT because TWRP had the same problem). The problem is not in the recovery, since they both don't work. Fastboot works (I could flash a different recovery). It's just that as soon as something tries to flash into /system, the phone reboots itself. I tried pushing the bootscreen via adb, but that gave a 'protocol failure.'

tl;dr: Phone reboots while flashing in both TWRP and CWM Touch, eventually it didn't flash anything at all.

I am beyond reasoning and have no clue on what to do.
NEC N21 > NEC N400i > Nokia N70 > Nokia 5800 XpressMusic > HTC Evo 3D > HTC One Black > HTC One M8 Space Grey

HTC Evo 3D GSM - S-OFF (Revolutionary) - HBOOT 1.49.0007
Main Rom: CMB PACman Rom
2nd Rom: Empty [for now]

HTC One Black - S-OFF
[ROM] ViperOne 6.2.1 | KK 4.4.2

HTC One M8 Space Grey - S-ON Unlocked
[ROM] ViperOneM8 1.6.0 | KK 4.4.2