Takes slightly longer to open than you might think. Like a few others on this forum, I had Rockstar Games Launcher telling me the game is already open. My "fix" for this was found entirely by accident, simply waiting. Yes, really. When the warning window popped up that the game was already running, I started checking my phone for something related to the issue. Around 30-45 seconds later, the game suddenly started without any further input from me. From now on, even though the game says it's already running and won't launch a second copy, I just have to be patient and wait for it to appear. I'd guess it should take no less than two minutes on slower systems, but I don't have any way to test or confirm this.