[MM3-users] Internal server error

My mailbox is filling up with dozens of notification of an internal server error. i wont post the whole mail as it is long, but here is the top:

Internal Server Error: /archives/list/jackrail-meta@jackrail.org/recent-threads

TypeError at /archives/list/jackrail-meta@jackrail.org/recent-threads 'datetime.date' object is not iterable

Request Method: GET Request URL: https://list.jackrail.org/archives/list/jackrail-meta@jackrail.org/recent-th... Django Version: 2.1.9 Python Executable: /opt/mailman/mm/venv/bin/uwsgi Python Version: 3.7.3

What is causing this? [Assuming that knowing the cause will lead to me fixing it.]

Andrew