I never traced out the Matrix 2, just the first one, and from a quick look it doesn't seem like they changed the button arrangement much. -
https://www.acidmods.com/forum/index.php/topic,34545.0.html might help in seeing if anything is way off. Some of it might be, as again that's for the first one.
Does pressing BK (Back) also press DR (D-pad Right)? or is it only DR that also presses BK?
If they did keep the same layout, that's an odd issue to have as those buttons do share a common connection, but pressing one should have no effect on the other one because of the Diodes D6 and D11. I'd check those to see if anything measures weird, but can't see how that would cause it.