According to the wiki, yes, the CELL is related with your issue but it has a lot of related points to check. It's also known that CFW has issues with PS2 games.
Downgrading to CFW 4.84 should give you a clue if it is CFW related or not.
Does this happen with PS3 and PS1 games?.
Also, how are you running your PS2 games?, via discs or through PS2 Classics loader?.