UPDATE!
The LSDJ cart started acting the SAME way with my other gameboys, so I replaced the battery and now it works on all of them!
The only thing I can note with the DMG is that when you start playing whatever notes you have tracked out, the contrast on it goes up a tiny bit.
Is this normal?
I still have the option to send it back to the person who sold it to me.
Should I do that?