calendar plugin no longer working with latest wp

I'm trying to find a solution for the following site where the calendar plugin has stopped functioning with newest version of wp

Plugin displays an image based archives calendar using this plugin -

It seems the CSS of the plugin some of it customised by the previous developer stopped loading as well.

The calendar can be seen in the sidebar further down the page here -

I haven't been able to find a replacement calendar solution which doesn't anything like this or a coded solution.

Your advice would be appreciated