It is logic that a warning happens when the name is already taken. Since you are using the same Database. to avoid confusion and error from the component, I suggest you to create a user for each game, with different suffix. like Bouma_swtor, Bouma_lotro. It is not GREAT, but this could help for now.
for the other problem, always make sure that the member/user is connected via the main page, meaning, the CommunityBuilder or Joomla login, and not any other com/mod. (example Kunena forum). for some reasons, Cache with Kunena not working perfectly.