Do you have other SmartApps installed? From what I remember when this has happened in the past with iOS all of the SmartApps have gone missing. There’s a variety of different reasons.
SmartApp Spaces in Icons
If you have any custom SmartApps installed, you can check to make sure that none of them have spaces in the name for the icon:
Incomplete SmartApp Installs
You can also check if there are any ‘incomplete’ SmartApp installations from the SmartThings IDE :
Samsung SmartThings Support
Alternatively, some people have just had to reach out to Samsung SmartThings support to get the Automations tab working as expected again.