Some of the planets added by Arcana are located in vanilla star systems, where as planets beyond tier 6 difficulty have their own unique stars. If these stars aren't showing up, it could mean one of three things: 1 - Some mod is overwriting Arcana and preventing the planets and stars from generating, possibly True Space. 2 - You are searching in a region of the universe that you've already loaded, meaning that no Arcana related stars or planets can be there. And 3 - The mod was somehow improperly installed and none of its content is appearing in the game