This is a very specific issue that involves linking Moodle to an OwnCloud instance.
We have a Moodle instance that is Moodle 3.11, I also have a Moodle 4 Alpha instance where the same issue occurs, but I shall stick to Moodle 3.11 and earlier.
We link Moodle to an application that is based on OwnCloud using the OwnCloud Plugin or the NextCloud Plugin. I need to stress that the plugin is not playing any role here since the issue crops up with either.
If I connect to my own OwnCloud instance, I get a file list after I have Authorized my credentials. However, If I authorize to the Larger application that is based on OwnCloud, I get no file list displayed. The process goes through the authorizing process, I even see the name of the application I am linking to, but I get no file list.
According to the owners of the application, a list of files is sent across to Moodle, it is simply that Moodle does not display the list.