First of all, I would move everything related to TU5 on the stick. My setup and the setup I always recommend is having two USB sticks with the very same structure: TU#, cache file, preferences, gamer account(s). On the hard disk you only have the DLC. That way there’s no way cache, preferences and gamer accounts conflict. The fact that the cache for TU5 is on the hard disk may be the issue.
Second of all, remember that every time you rebuild the cache, you lose all your offline scores, which is all scores for customs. So, the motto is: never rebuild your cache.
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!