CSC515403. Avoid system list urls for the custom list instances
Some of the OOTB feature just break, as you have already have "custom" lists with the same "system" urls. Also, you features cannot be activated, if you already have some of the OOTB SharePoint features enabled - huh, you already have OOTB
Pages/Calendar e.t.c. lists/libraries.
Do not use system url for custom list instances.
No links are provided.