Folders disappear then come back

I'm not sure at which point this behaviour started, it was either after thunderbird suggested that I compacted my folders or perhaps after the update to the latest Thunderbird version. Sometimes when I start Thunderbird I only get the inbox (which is empty) . Sometimes I get nothing then the inbox gets downloaded from my IMAP account. Sometimes I see all my folders for a few tenths of a second and I see message on the bottom border (where it normally talks of connection to the mail server) but these messages talk of deleting all my folders one by one. On one occasion all my folders were laboriously downloaded one by one (as reported on the bottom line.) Often shutting down Thunderbird and opening again results in all the folders being instantly available (so they must have been there all the time). It sometimes takes a number of shutdown/restart cycles to get the email folders back. Any ideas what is going on and how I can stop it happening? Thank you for getting this far.