Multiple attachments sent with every notification

Sometime over the past weekend (Nov 28-30), email notifications starting including many attachments, often over two dozen. Most of these appear to be the same attachment of the poster's photo. Others are icons for a comment, the issue type, the issue priority and the Atlassian logo.

All this despite requesting that the email notification be sent as text only. I also tried selecting HTML notifications in my profile, but the problem persisted.