I've installed Thunderbird 60 a few weeks ago. I used the older version because I needed the add-on for importing mail from Windows Live mail. This add-on doesn't work with the latest version. After the automatic Thunderbird update from 60 to 68 last night all imported mails are lost. But not only that, now, all "sent" mails (apart from 3) from the last three weeks since the Thunderbird installation and all mail addresses that had been added to the address book since then, are lost as well. The respective folders where the missing mails are stored, are empty, so this is not just the problem that the mails are not shown.