I'm using Blender 2.83 on a Mac (OS Catalina 10.15.5) Every time I try to navigate out of camera view, everything disappears. I have "Orbit Around Selection" checked in my preferences, I've repeatedly tried frame all in view and the other navigation shortcuts to reset the view and nothing helps. When I go back to camera view, everything is there but the second I try to navigate around the model, the same thing happens. Am I forgetting to do something I was remembering to do yesterday?!
Actually I may have solved my own problem but wanted to keep the question active just in case anybody else was experiencing the problem. Turns out "View All" did end up solving the problem but I had to actually use the Home button rather than selecting the menu option. Live and learn! – Jim McNeill