Just wanted to add that I had a similar issue attempting to migrate the
Cyrus 3.6 in Debian. After the upgrade it was possible to log-in and
receive e-mails but all existing e-mails and sub-folders were no longer
visible.
In case it's helpful to anyone, I ended up downgrading back to Cyrus 3.4
from the bullseye-backports release. I then used the reconstruct command
to rebuild my mailboxes which managed to get everything back. However, I
guess sub-mailboxes were given some sort of new unique identifiers since
my IMAP folder subscriptions were lost, which I initially mistook for a
failure to reconstruct the sub-folders.
In addition, I got some new mailboxes which were erroneously constructed
and were difficult to delete both due permissions issues and the fact
that their names contained unprintable characters.
