Volume control on apple wireless keyboard are not working consistently

I have the most recent OS and all available updates. This issue has not happened until recently (within the last few months) and I've owned the keyboard for a while. I have times when the volume controls on my apple wireless keyboard do not work. Usually if I restart my computer they will restore. I've never had to restart my Mac so often until recently and it is only for volume controls. I restored keyboard to default (it hadn't been changed) and it still does not work. Why?