This is the fourth instance where I'll be working on sheet metal part when suddenly a face of the solid body will disappear. This leaves a "hollow-shell" format that is difficult to work with. The most recent case occurred when I was adding parts to my part file. One picture depicts the hollow area where I can now select an internal face. You can even see the edges of a countersink hole. The first picture displays what the part should look like. These parts were originally made in SW2016 but we have recently updated to SW19. The issue occurred before we updated to SW19.