on a SharePoint site (SP 2016 on-prem) we have one calendar which is accesible also as a Web Part on the site and is wokring o.k.
If we add a second calendar, the calendar itself works o.k., but if we add this second calendar also as a Web Part on this site, there are no "+Add"-buttons visible and we cannot click into the Calendar Web Part, seems as if it were frozen. If we open the second Calendar itself instead of trying to use via Web Part, everything works, trhe "+Add" buttons appear and the Calendar is clickable. Via "Edit Page" you can also see that everything works, the "+Add" buttons appear and the Web Part is configured for "Full toolbar". After clicking on "Save" in "Edit Page"-mode and returning to the normal view, the problem still occurs.
Any idea? The problem only occurs on one site within the site collection, on the other sites we can add multiple calendars and use them also via Web Part. I suppose, users misconfigured something in the default view for calendars, but I can't find the error....