Well, I succesfully opened my Reaper v5 project with Reaper v4.22 (without any compatibility issue) and clearly saw that all my notes were misaligned (regardless of what Reaper v5 was telling me). I deleted and recreated notes and fills and now it works.
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!