Just tried to import two GPX courses from my iCloud drive. Did not work, the icons are being displayed but tapping on them does nothing. Import via mail did work flawlessly. As I am new to WOD, I only imported a course once, but not sure if I did this via iCloud drive or mail.
iOS 13.2.
The GPX import problem is a bug in iOS 13 that myself and many other developers have been telling Apple about since June. It seems to be related to what other apps that accept GPX are installed and the order in which they were installed.
The bug was initially when sharing GPX files to the app, but when Apple broke that I added the Import button on the Routes tab as a workaround. However even that does not work for some people. In that situation the only workaround I know is to reinstall the other apps that appear in the list when sharing a GPX file (do not reinstall WorkOutDoors).
I realise that this is not viable for most users so I have changed the Import screen in the next version to allow any type of file to be imported, in the hope that works (it is difficult to know because the sharing and importing works for most users, including me).
Sorry about that. Hopefully Apple will fix the bug soon. iOS 13 and watchOS 6 are the worst versions I can remember of either operating system, and I have coded for all the versions of both of them!