Just to clarify, when you go to the contact, click on edit or during original input click on view more, and when you click on the ringtone option, are you then clicking on the + sign?
Are you trying to set custom ringtones for apps or for contacts?
I'm trying to set a song from my phone as a my general ringtone and I'm also trying to set custom ringtones for my favorite contacts. I have no custom apps on my phone nor have I customized anything
Where are you getting your custom ringtones from?