S5 Back key question topic

Twice now in the last 48 hours my back key has stopped working. Nothing no lights no response.

The menu key works fine and as soon as I restart it comes back.

I don't think this is a hardware fault as it comes back straight after a restart and the other key works. Am I right in saying that software can have a effect on the touch keys ? Or is it something else.

Oh just to mention I do have a tempered glass protector on could it be confused with it on or is it just software.

Thanks