See this general article https://support.mozilla.org/en-US/kb/troubleshoot-mode-thunderbird#w_the-problem-no-longer-happens-in-troubleshoot-mode But I have a suspicion: have you activated the "Quick Filter" bar in the thread pane? Since if you have activated the button "Show only unread messages" but your folder doesn't contain any unread mail the thread pane will be shown empty! And if you have also activated the "pin" button "Keep filters applied when switching folders" you may never see any messages in your folders. In TB troubleshoot mode toolbars and settings are reset to standard values. So your Quick Filter toolbar settings will be disabled, and TB will display all messages in all folders

Other possibility https://bugzilla.mozilla.org/show_bug.cgi?id=1952311 Have you compacted your folders recently?

Hi Mapenzi Thank you for your response, but it doesn't help. I often use the filter function, but did not this time, and the filter field is blank. I don't know where the pin button is for "Keep filters applied when switching folders." I assumed that in troubleshoot mode that some functions, like filter, got disabled and that is why it allowed me to see messages.

Hi Mapenzi Thank you for your response, but it doesn't help.

Did you read the SUMO troubleshooting article I linked in my answer?

What does Troubleshoot Mode disable?

  • Add-ons (extensions and themes)
   • Hardware acceleration
   • Window and sidebar size and position settings (described in terms of Firefox)
   • userChrome and userContent customizations ; see userChrome.css and .js and userContent 		
  are unsupported
• JavaScript Just-in-time (JIT) compiler

Sorry, I forgot to mention I did read the article. No themes or extensions. I tried turning hardware acceleration off, but didn't help. BTW what does SUMO stand for?

SUMO = Support Mozilla

Start TB in Troubleshoot mode again. When the "Thunderbird Troubleshoot Mode" dialogue box appears, check "Reset toolbars and controls" and click on "Make changes and restart". Are your messages visible now? Are they still visible when you quit and restart TB?

Hi Mapenzi My apologies for the late response. I left for a 2 week vacation the same day as your last post, so I just got to trying it today. In any event, checking Reset toolbars and controls did the trick. It works after restarting TB, and even after restarting my computer, just to be sure.

Thank you for your feedback, I'm glad I could help solve your issue.