The Samsung Galaxy S8 and S8+ are some of the fastest devices on the market but even these suffer from the occasional bit of lag. Most would put it down to Samsung’s TouchWiz user interface that the company apply over stock Android, and you wouldn’t be wrong.
It seems that Samsung have identified an issue with the TouchWiz Home app that could contribute to lag on the Galaxy S8 and S8+ and have released an update to address the issue. Samsung TouchWiz Home v6.1.09.2 has clearly highlighted in the changelog notes that the update addresses an issue when swiping up and down between the homescreen and the app screen. It also improves the visibility of app names under icons against a white wallpaper.
The update to TouchWiz Home should be available now for your device either in the Google Play Store or via the Galaxy App.