First I left my world via 'Save and Quit to Title' with a resistance 5 effect ( /effect epicbob57 minecraft:resistance 1000000 4 true ) When I reconnected, a spider nearby hit me and instantly killed me (I was in survival mode). The 'Respawn' and 'Quit to Title' buttons were grayed out as shown in attachment, and so I had to Force Quit the application to leave.