I have a workbook with 7 sheets, 3 of which are hidden and the other 4 all
have pivot tables. The workbook automatically updates the pivot tables based
on data that gets copied from external spreadsheets and pasted onto the 3
hidden sheets.

For some reason, when I open the workbook (and after everything updates,
without any problems), I am unable to select a different sheet than whatever
the current sheet is. I can select other cells in the current worksheet just
fine, but can't switch to another sheet via clicking on its tab (nor can I
minimize or close the workbook itself with the buttons on the top right of
the window). However, when I minimize Excel to the taskbar and bring it back
up again, I can change tabs to my heart's content. The workbook is not
password protected in any way so I'm confused as to why the other three
worksheets seem "locked" at first.

Any ideas what might be causing the issue?

Thanks in advance!