In addition to this, I did a “repair folder” and now the same older emails with no content have disappeared. So again, how can I fix this?

Hello there hiehrer. We have read your message. We try to help you.

Try to reset toolbars and controle to resolve the problem. Is a option

Or you can right click on the folder and select properties and then the repair button to re-index your mail.

https://support.mozilla.org/en-US/kb/thunderbird-crashes What crashes did you had?

Please report to us your crash number with pop up text

Greetings Firefox volunteer.

It sounds like your mail files got corrupted. Depending on the state of corruption using "Repair Folder" may erase messages from the affected folder which cannot be recovered anymore. In other words, the damage was already done, and by using "Repair Folder" Thunderbird did attempt to repair the damage and get mail files back into a consistent state. In that case you'd need to restore the lost messages from a recent backup done prior to the corruption.

Corruption is often caused by anti-virus software messing with Thunderbird mail files. It is therefore recommended to create an exception for the Thunderbird profile folder, so that the real-time scanner won't attempt to scan the profile with your mail.

For more information on the profile location see http://kb.mozillazine.org/Profile_folder_-_Thunderbird

Also see http://kb.mozillazine.org/Keep_it_working_-_Thunderbird