A group of explorers discover a previously uncharted island, only to discover the terrifying reason why it wasn’t discovered earlier. Now, trapped, they must find a way to escape the island’s horrors.

Hello, the last rewrite is much better, still it seems to me that it's too vague to create interest in the reader.
I personally don't like expressions like "change himself in the process" because it's more a promise of what you want to do than a proof that you master your story. All movies show some kind of "change" so it's useless to talk about it in this vague form.

Can you be more specific about what constitutes "terrifying things"?? I'm not suggesting you reveal everything, but you need to reveal enough to wet the appetite, to make a script reader curious enough to find out more..? And I don't think "terrifying things"? does the job.

Much of this logline is redundant as most of it doesn't describe a plot. The entire first sentence can be cut, and the second sentence lacks a main character. Can you specify one character through who's point of view the story will be told through? Re structure the logline around that character, their flaw and goal.