KeeFer

In your main game directory, scroll down until you find GTA5, right click on it, then select properties, then select compatibility, you will then see a box you can checkmark to run as administrator, remember to hit apply before closing out.

Hey, hope this helps, (if you haven't solved it yet) I had this same issue out of nowhere with my game, GTA would say it crashed as soon as I fired up RPH, and would stay on a loading bar saying it crashed and was trying to collect report, after trying a couple times to get it to launch, I decided to go to the main game directory and select properties on GTA5 and then select run as administrator, then hit "apply" then launched the game with RPH, I was able to load in without crashing and play without a crash, not saying this will work for you as it did for me, but it's worth a shot if you haven't tried it yet or figured it out. I also run RPH as administrator or else it won't let me launch story mode with RPH. I'm on GTA build (3504.0)