GTA Crashes on startup, claims GTA is already running

GTA V will not launch at all, with absolutely nothing besides LSPDFR installed, all launchers up to date, so on, so forth. Every time I attempt to launch the game, without fail, it will briefly open the Rockstar launcher, before crashing altogether, with an error message at the bottom. This did not occur prior to downloading LSPDFR, and continues to happen even after redownloading GTA, and not even going through LSPDFR setup again.
 

Fixes attempted included closing GTA V through the task manager, verifying the GTA V files through the Epic Games launcher, redownloading GTA V, redownloading the LSPDFR setup, restarting my computer, and redownloading the Epic Games launcher entirely, all without any success.
 

Error message reads out as: "An instance of Grand Theft Auto V is already running. Please allow the game to fully exit before attempting to play again. If you believe you are seeing this message in error, please check the task manager for any running instances of the game or try rebooting your computer. If you continue to see this message, please contact support."