It could be your cache got lost/cleared out at some point. Let it cache just the DLC and not the customs, move it over to your Title 5 stick, and then load it up again and see.
You are about to leave Rhythm Gaming World and access the external songs DB. While no song or file sold for commercially available videogames is hosted there and only fan generated content is allowed, Rhythm Gaming World has no direct control over the database and no files are hosted here. Alright, we had to made you aware of this, now you can visit the database!
