Hey @Wade , I recently had the same problem and find out that "Rocket League" Launcher was in the "Applications" folder located in MacintoshHD/Users/myuser/Applications, it's at the same location as Documents, Downloads, Desktop etc. It is not the same folder were all the mac applications go.
So I Uninstalled Rocket League and deleted that launcher, also create a new bottle in Crossover for heroic.
Then I reinstalled the game and it worked perfectly.
Hope this could work for you!