Figured I'd put a little update on this, today I ended up moving all the parts into a wooden box I made in advance for it, but once all was in there I encountered endless flickering and blinking again, random leds on the strip stopped working etc or just blinking a super dim red light.
To check if it was my strip shorting or anything I compiled some custom direct color testing scripts to the Arduino and it colored perfectly every single led so I assumed it was not the lack of power or anything defect on the led strip itself, but something in the box/interference.
Out of endless testing I took all parts out again from the box but blinking was still persistent (blinking constant green now on NTSC, white on pal I think).
Just to have given everything a try I glued a layer of aluminum foil to the back of it where circuit board etc are mounted, did a test with those mounted in there before I put everything together again, blinking was still persistent.
Figured I just put everything back together and wait for the level shifters I ordered to arrive and hope that fixed the issue, last test before giving up on that for now, everything mounted in the box it suddenly worked again, well partly, still lacking a few leds on the end but blinking have stopped, I don't know if it's a coincidence or not, I noticed that when even just securing the cables up to the frame to the wall there was some flicker while touching them.