KB4011091 is the ticket. Uninstalling it allowed the shortcuts to start working again in Outlook 2016
Hi,
Please refer to the KB article below:
Your form cache is probably corrupt
metalogix.force.com/.../Your-form-cache-is-probably-corrupt-message
Regards,
Cyrus
It looks like removing KB4011089 resolves this issue with missing attachments in Outlook 2010.