Update!
I've removed all pack adjusters from my main GTA V directory, and my game has successfully launched.
The adjusters I removed:
GTAV.ResourceAdjuster
HeapAdjuster
PackfileLimitAdjuster
ResourceAdjuster
SirenSetting_Limit_Adjuster
WeaponLimitsAdjuster
I'm not sure which exact adjuster is the issue at the moment. I'll test that later.
The newest LSPDFR and Script hook V. Mods folder was renamed to _Mods after being updated, and RPH was set to load the game without any plugins. My AV did not block anything from RPH.
Any help is greatly appreciated.
Check Open IV to see if any RPF's in your mods folder need updating. Make sure to put it on edit mode and a prompt should appear on the top of your screen.
If not, rename your mods folder so that the game won't load your modified files on startup, and see if your game loads.