That would do it.

^^ One of the dmg's traces on the ribbon cables is not broken, but bent in a way that when I secure the ribbon cable to the rear pcb, they bend back. Maybe this is the source of the problem

Check your ribbon cable. It may have been folded to much and a few traces have broken.
If you notice in this picture, up and select are linked to the same trace.

You can replace the ribbon cable but it can be tricky especially if you already have a backlight in there.

Oh, I picked up a DMG once that had this problem. The solution I found was to swap the front cover with another one. Some how the plastic was warped in such a way that it affected the button press.

hmm.... maybe they're still a bit rough from the mold? use some sand paper perhaps?

the plastic buttons wouldn't cause this, the silicon is the part which makes the electrical connection, the buttons themselves are within a very small margin of the originals if not exact.  if they were too thick, there would be an issue with getting the tactile feeling from the silicon pads in general, but a connection issue (electrical) when they are pressed would be a silicon issue. or else dirty contacts.

it could perhaps be the backlights though, if there is created pressure.  i've had this issue myself a long time ago with a thicker model, the pressure caused the buttons to be wonky...

try reconnecting the ribbon cable inside, it may not be making good contact and you could be having button issues from this.

It could be, also make sure the silicon pads are aligned correctly. I've got a DMG with one of kitsch's backlights and I didn't have to worry about it being to tight of a fit. You could always loosen the screws on the lower half of the PCB just to be sure, it won't hurt it if they're let out just a tad. Also, did you clean both the silicon pad contacts and the PCB contacts?

I have seen a thread about this I think on 8bc, but I cant find it anywhere. I recently backlit 2 dmg's and replaced the buttons in both with some of kitsch's. In one dmg the up arrow is finicky and I have to press down pretty hard to move the cursor in lsdj. In the other one the select button and the up button does not work at all. Ive cleaned the contacts with alcohol. Could it be because of the tight fit with the backlights? Thanks for your help