Invisible bosses

[Kasei]

Like the title says, some of the bosses when playing this are invisible. Sometimes it's just a part of it (the end part of the tail for the centipede boss), sometimes it's during some attacks (the mantis boss is invisible for all but certain attacks), and sometimes, like for the final boss, all you can see is his hair floating, and his shields. For normal mode this wasn't much of a problem since I didn't really need to see them all the time to win, but now that I'm replaying it on nightmare it's more problematic, plus it would be nice to get to see the bosses properly. I've tried changing a few of the graphical settings, but with no luck.
Does anyone know how I might be able to fix this ?

[Quint the Alligator Snapper]

...you were able to beat anything with invisible parts, even on normal? Hot darn.

[Kasei]

On normal it's not too hard, since you can still see the projectiles, but on Nightmare I really need to see what the boss is doing so that I can predict and avoid attacks properly.

[LazyVista]

Thats odd, you can always do a desperate attempt and just simply reinstall the game