video shot is missing in the export

Whenever the application crashes you should reset the preferences. Hold ⌥ ⌘ as you double click the library you want to open to launch the application. A dialog appears asking you if you want to Delete Preferences. If you don't do this while double-clicking your library, the application will open a default Untitled library.  

Select the project in the browser and use the Share function from there.

If it still doesn’t work Delete all your library generated files from the File menu.

Did you recently update or upgrade this Mac? I see many "?" icons in the Dock.

Whenever FCP crashes or starts acting strangely an easy thing to try is resetting the preferences. Hold option and command while launching FCP and choose Delete Preferences. It will open the default Untitled library. Re-open the library you were working on, set the preferences back to the way you want (disable background rendering, etc.) and see if the issue has been resolved.

Can you post a screenshot that shows the area of the timeline with the missing items? I assume you can see then when you play the project in FCP.

Please use command-shift-4 and drag to take a screenshot. Easier to do and will avoid twisting our necks... 😎