Outlook 2011 for Mac with IMAP and POP – POP disappears

I have Outlook 2011 (yearly download subscription) on my Mac Tower.  I have 3 accounts loaded on Outlook  – my main one is a POP3 and 2 others are IMAP. However at random times, when clicking on one email or another, 2 accounts disappear, including my POP3 account’s emails.  The only way to get the POP3 to reappear is shut down Outlook and start it up again. 

This “solution” is aggravating and time-consuming.  Is there any way to get this account back without restarting?

The POP3 account is NOT found in Windows drop down menu nor in the navigation pane.  Strangely but perhaps related, there are a(n increasing) number of “Recovered Folder”s in the ON MY COMPUTER section of the Navigation Pane – but all files seem really old and incomplete. 

Please help.