Probably easiest just to show you a video of my problem!
That 8x8 LED matrix board does not have 8 anodes on one side and 8 cathodes on the other side.
The layout is like this:
R6 R3 C4 R1 C6 C7 R2 R4
---+---+---+---+---+---+---+---+---
C1~8 = Columns / Anodes,
R1~8 = Rows / Cathodes
---+---+---+---+---+---+---+---+---
R8 C5 C3 R5 C8 R7 C2 C1
The 3 LEDs you see blinking are probably on C4, C6, C7.
Ah... Awesome, let me try again!
All working fine now, thanks
If only all solutions were so straightforward!
Just thought I'd give a quick update and thank everyone for their help thus far...