I created three subfolders in the archive folder several months ago, and moved a lot of emails from my inbox to the archive subfolders. Everything was fine, and a few days ago, I noticed that two of the subfolders contents are all gone. I tried the "repair folder" option when right clicking on the folder, but this did not do anything. I haven't tried anything else yet, aside from rebooting and restarting the Thunderbird program a few times.