Okay, I'm making a 2-player co-op map. The two players are Player 7 and Player 2. Player 7 is required, Player 2 isn't.
It seems that on cutscenes, for one of the players, triggers that make the players center view onto a location or text triggers don't work. I know that it's for one player becaues when I test alone as Player 7, I can see them fine, but when I have both Player 2 and Player 7 in play, I, player 7 can't see the triggers work.

What causes this, and more importantly, how can I fix this?

Double check your conditions. You've more than likely got some switch being set so that you don't see the same message twice, which makes the trigger run only once. You want it to run twice.

As a cardinal rule, a trigger that doesn't run is due to conditions not being met or wait blocks. Sit down and THINK about the conditions, and which ones might be set prematurely, then fix them. If all else fails post the trigger and I'll tell you what's wrong.