One of my ram bay one accepts 2 gb stick

Hey all, trying to revive my old 2010 uni body 17inch here.

Before I've always rocked a 6gb ram (4+2) and after trying to replace the 2 gig stick with a 4 gig, the macbook gives me the ram beep and will not post.

As I've accumulated a shocking number of ddr3 ram sticks, I've tried them all, and the onky ram bay 1 of my macbook accepts is the 2 gig sticks (I have 2 identical ones and they hoth work)

But when I try to introduce the socket to a 4 gig stick, it suddenly refuses the ram, even if all I'm doing is swapping the previously working 2 gig and 4 gig ram sticks around, one bay happily access any size ram, but the other only accepts the 2 gig.

The macbook even boots with only the 4 gig stick but not if it's in the problematic bay.

The rams I'm testing with are the correct voltage and speed, I'm a bit confused as why it's happening here.

Any ideas would help.