Murphy’s Law is right! I have a similar setup to yours using OnSong to control my BB although I don’t control tempo. After several months with no problems suddenly today when I was going to practice my BB only changes songs intermittently when I change songs in OnSong. I reset all the connections, checked my midi in OnSong, checked the BB midi settings, and I see that OnSong is sending data when it changes songs but… the BB only changes songs intermittently. What’s weird is that all the other CC’s work with no problem.
The way my setup works is I press a switch on my midi footswitch, OnSong goes to the Next Song, then the song’s metadata sends whatever CC’s I want to send to the BB.
I remember I had this exact same problem when I first started using midi to control the BB and somehow it went way but I never actually knew why. Now all of a sudden it rears its ugly head again.
At least I can still physically change songs on the BB but as you allude to, it’s very disconcerting when nothing has changed then something just stops working. I know there are midi sniffing tools so I guess I’ll have to get one and see what’s going on. I need to make sure OnSong is sending what it should although I am assuming it is since all the other CC’s it sends work like they should.