It is the phone's settings.
I suggest you change the time out to 30 minutes or longer.

That is what I did. I also programmed the Power Button for Instant Screen Lock.

that way, I get the best of both worlds.

 

I have the same problem with not being able to give voice commands through a Jabra bluetooth hands free device to my locked Galaxy S5. Playing with the lock settings is not a good answer for me. My previous android phone accepted voice commands while locked.

Is there a way to enable bluetooth voice commands while locked? Is there a way to get Samsung's attention to fix this?