I have problems with transferring midi to Riffer in Reaper. First of all A#6 you suggested didn't work. Experimenting I found that A#7 synced with Riffer. But transferring midi either directly from at track in reaper or from a saved midi file through media explorer (Windows mode), both using ctrl+alt drag as usual doesn't work. Some notes appear but other are missing, and the tempo is wrong. I have tried with all sorts of number of bars and tempos (wondering why you have all those 8/4 loops). I created a project from scratch to exclude hidden/forgotten settings, but still.
Finally I started up the latest version of Cubase, and it worked fine. It transferred correctly the same .mid file that went wrong in Reaper. It also responded correctly to A#6.