Volume control will often stop working, if your sound server (normally pulseaudio) dies or restarts whether by itself or by you. The reason pulseaudio may need to be restarted is due to some sort of crash or other issue that prevents sound from working (normally restarting or doing a killall pulseaudio fixes things).
However, you will normally find at least in OS's like Ubuntu/Mint 16/18+ that you cannot control the volume whether adjusting the level, changing input/outputs and........