Getting a 404 error on auto-generated archive link (in wp widget)

I’m using the wordpress archive widget in my sidebar. The permalinks are set to the format:

All of them work except January. I have not set any custom links or changed any settings.

My website is

Please navigate to the archives section and click January to see the error. If on a phone, it’s at the bottom of the page. If on a computer it’s in the right sidebar.

Why is this happening and how can I fix it?

Thank you!