After becoming the League Champion and defeating the final Hurrah Island challenge Prof. Kukui allowed Sun/Moon and others to travel to the Unova Region for a year and test what they learned in Alola. Your rival Gladion followed and together you chose new starters for the journey across Unova. Rumors say Team Skull has also been spotted in Unova. Sun/Moon was also granted permission to enter the Regional Tournament at the PWT representing the Alola region if they defeat the Unova Champion!
Note that all homemade Pokemon games are not officially produced. They are games produced by individuals or teams. Just like programmers writing code, there will not be a perfect game, even officially released games will have bugs, if you encounter problems in the game, please seek help from the pokecommunity community and the author of JrFort & Aster who made it.