One (or More) of Your Sheets is Not Visible in Paper Space
Issue
You are unable to see one of your sheets in Paper Space. The sheet may be able to plot, but it's still not visible in Paper Space.
Cause
The Model/Paper toggle is most likely set to Model for that sheet.
Solution
With the problematic sheet open, examine the multiple toggles in the bottom right corner of your CAD window. One of the toggles will read either MODEL or PAPER.
Even though this sheet might look like it should be viewed in Paper Space, you might have it set to MODEL for some reason. This setting makes the sheet invisible in Paper Space.
To correct the issue, click the word MODEL – or type PSPACE in the Command line – to toggle this setting to PAPER.
Your sheet should now be visible in Paper Space.