Holy ****! I found a defect on the PCB and fixed it. I need Oddforge or Zefyr to confirm this is a good fix.
I spent the whole night using a multi-meter to see if I could figure anything out. I noticed that on most rows, the bottom end of the diodes on the same row connects to each other, except the HJKL; row. And I checked that they do connect between ; L K J H, but not between " and ;.
At first I thought the via was plugged and causing the problem, but when I looked closer, the trace is actually disconnected (at the red rectangle). I jumped and connected these points and looks like all the keys are working now.
I am glad I fixed it. But I am mad that the PCB is defective, and caused me so much grief...
Can I get a replacement PCB?