Okay so my first test was to unplug the PI from the end of the string since that was the easiest and now all 9 light up!!! Any ideas why the PI at the end could be causing that? I did make the cable myself so was thinking I somehow reversed polarity but I checked that and no issues.

Could something actually be wrong with the last pixel where it won't pass the voltage? For now I just kept the PI at the end disconnected, if I go all white there is some flickering so I would definitely need that PI at some point, but luckily none of my sequences have full white so it shouldn't be a problem.