Some archive by year page return 404
When clicking on archive in my wordpress blog I get a list with links to different month, e.g.,
October 2020, …, June 2019, …
When clicking on a month I get a view with posts whichs were published in this month and the breadcrumb creates a link to the respective year. While all year-links work, the link for 2019 return 404.
I have no idea where to start to fix this error. Do you have an idea why I get 404 for this specific year?