I had lighting set to turn on/off with at sunset/sunrise, and it stopped working after over a year of working fine. I completely deleted the automations and recreated them. I also rebooted everything associated with SmartThings (router/modem/hub). I also killed power to the smart switches.
Nothing works. I’ve e-mailed Samsung three times. Once they responded with instructions completely related to something else. And, of course, they don’t answer the phone.