Ps2 has modchip, can read original games, but doesn't read burned games.

Hello! New here. I just got a fat ps2 (SCPH-39004 PAL) from a relative, which I used to play with when I was young. It has the cut on the warranty sticker and an additional sticker of the person who modded it, so I know it has a modchip. I also know that I used to play burned games in it, I have evidences of it. Yet, after years of not playing with it, I cannot seem to anymore. I have only 1 original ps2 disc, which works with no problems, but none of the burned discs I have seem to work.
My...

Ps2 has modchip, can read original games, but doesn't read burned games.