I purchased Storm Island on the release day. I played it, and the game was fine - no problems at all. Then a family member signed in with their account, logged into the game and tried to play Storm Island for the first time. They were able to travel to the island, signed up for the first event, didn’t play it, and left the game. Upon return to the game a few days later, the same family member tried to play again, but as soon as they got to the island, the game crashed and sent them back to the Xbox ONE dashboard. I uninstalled the FULL game and re installed it multiple times, but that did not solve the problem. In fact, it made it worse, because the crashes started happening every time they exited any garage. In the meanwhile, I was still able to play Storm Island with my account on the same console with no problems.
After trying every possible solution that was mentioned on the forums and elsewhere on the internet, I decided to delete the Horizon 2 saved data of the second user (not the game install, the game save itself) from both the console and the cloud. Of course, all the cars disappeared, all the game progress disappeared, the driver level was reset to zero - you are basically starting a brand new game. The user started the game and followed the game instructions one step at a time. They played the game normally, and around driver level six, Storm Island was unlocked, and they were asked to go to Storm Island. Once they got there, they finished the first event, drove to the island garage, put on some upgrades, left the garage, and then left the game,. Once they started playing again, none of the freezing or crashing issues happened after that.
I’d love to hear if this works for anyone else, but be aware that you will lose all of your money, cars, driver level, and game progress.