You may need to be using the new V3 app. They’ve said that they are going to discontinue the V2 classic app, although they haven’t said when, but they’ve moved pretty much all of the support for Samsung brand smart televisions, vacuums, air-conditioners, etc. to the new app.
You can use both apps at the same time, but you probably won’t be able to use the Samsung brand devices in the old app anymore.
FAQ: how to tell which version of the SmartThings mobile app that you have