Admin area where users are able to make menu edit changes to menu links e.g. /admin/structure/menu/manage/main seem to break core functionality when appending the forward slash to node references. The following steps will recreate the issue.
Steps to recreate:
1. Visit admin/config/search/path
2. Click on the ‘edit’ operation, assuming there are existing menu links created.
3. Append the 'System path' field value with the forward slash character ’/‘. e.g. /node/1 will become /node/1/
4. Save the changes.
5. Visit any page that contains the main menu and you’ll notice the url alias no longer working. The link will now reference the node path with the ‘/‘ prepended.
Note: Please be sure to disable all all caches, and will need to re-save #3(no edits) in order for the '/' to be stripped, as the '/' is stored in the database.