If I right-click on any key in the main window and select "Open Key URL" I go to https://pgp.cs.uu.nl/stats/ (for the specific key id) which reports "Gone   The requested resource is no longer available on this server and there is no forwarding address. Please remove all references to this resource."

This seems like the same problem handled by Commit f3750133 authored 4 years ago by Rolf Eike Beer.  

This URL comes from kgpg.kcfg section group Servers, entry InfoServers.

Removing the first server, the second one works fine - but I suggest changing the http to https for the  two remaing servers, as well as changing the separator between them from a semi-colon to a comma.

Minor additional point - I suggest changing the menu entry from "Open Key URL" to something else, as it isn't really the URL of the Key, but showing the key's information from one particular key server.