I’m experiencing the same issues with multiple instances launching and not completely quitting with Early Access 2. It doesn’t happen every time now but enough to be annoying.
Additionally, when I double-click projects listed in the Epic Games Launcher app, Finder is brought to the front and nothing else happens. Double-clicking the .uproject file does nothing. The only way to load up a project is to launch the engine and select from the project manager window.
Another way to force quit is to right-click the dock icon and hold down option for the alternate menu item to appear OR Control+Option+Left-Click the dock icon.