Can't use back button on Galaxy S8

[AC Question]

Hi there hope someone can help. My phone randomly decided to stop me being able to use the back button on quite a few of my apps. Is there anyway to change this?

 

[ihearlivepplz]

1. We're you able to use the back button in the apps before? (some apps disable it to prevent exit)
2. In the apps where it does work, does it work consistently? (Check at least 20 times)