Certain apps occasionally won't unhide once hidden
I'm getting this situation as well. The ways I've found to make them show again after switching to each app is either
- Selecting Window > Zoom and then resizing it after it appears, filling the screen.
- Selecting View > Enter full screen (or ^-command-F) then exiting full screen.
I haven't found a way to prevent it from happening. It doesn't happen to every app or happen every time I hide apps and close my laptop.