Blog Missing Sidebar
Is it possible you have the sidebar disabled under:
Appearance → Theme Options → Blog Options
Hide the sidebar on blog home (useful for some layout styles)?
I'm unable to reproduce this locally.
Any chance you could PM me with a temporary wp-admin and/or possibly FTP?
I pushed up an update to 5.6.7.
We just migrated our server last night, so hopefully everything goes smoothly with the upgrade process. Please let me know if not.
Here is the new sidebar.php:
Thanks for your patience.
Either way is the same effect.