It just happened to me too!
My ghost hunting was working perfectly until yesterday. Today, my game crashes when i tap on my ghost hunter. After I reopen the game, all my Sims stop what they are doing. So all my progress is gone. I was almost finishing a 12h task and a 8h task, all related to challenges. I also had Sims working and they are back in the house - with their work clothes on!
I am submitting a bug report.