I followed the step below, then I could add the app to never sleep list. not sure how it helps but will give it a try. https://forum.developer.samsung.com/t/unable-to-add-app-to-never-sleeping-apps-list/11663/16 " previously set the app to "unrestricted’ in app info > battery. I changed it back to “Optimized” and then it showed in the list again. " That did it! Changed to "Optimized" under battery in the app. Went back to check the "Never Sleep List" and it allowed me to select it. Thanks for the tip!
