I had my LAN (playing with family. 2 People including me in one world) open and when I clicked the save & quit button, it just stuck there. The world saved but Minecraft refused to go back to the title screen forcing me to kill Minecraft. This also happens without having my LAN open. It also happens on my Windows 10 PC. I am willing to also give you the specs of that computer as well. (Windows 10 PC has much better hardware than the Ubuntu computer but it makes no difference)