two navigation keys at bottom of my s7 stopped working

[AC Question]

will not go back to previous screen. will not close all open tabs

 

[mhinc]

will not go back to previous screen. will not close all open tabs

This happened to me on a Note 5. You can try a factory reset. If that doesn't work, it is hardware. Which was what happened to mine.
I ended up having to send for warranty repair