Hi there,
The same problem with mid 2010… I have two identical 4 gb rams from the same computer working fine. One (any of two) 4 gb ram working fine with 2 gb for all slots combination. The result, you can reach only 2+4=6 gb
The main issue is that you can use only one slot for a new ram. The other must be 2 gb or maybe an origanal/specified label etc ram (this part i didn’t test)…
To sum up, what we can reach are (2+4), (2+8), (2+16???)
İ can see the effect of (2+2 to 2+4) 2 gb increase to some extend but it’sad for apple.
Does anyone can uptade or help with this topic?