Hi Stephen,
Could it be that certain Registration Bank files in the User drive of the Genos or on the USB stick used have been renamed or moved? Or maybe you are currently using, not the original USB stick on which the original Registration Banks linked to SB+ are located?
Try re-linking a Registration Bank from SB+. Does it work as expected (in both directions) then?
Since it "sometimes" works, there shouldn't be a problem with the MIDI connection. Basically, I recommend activating the preset MIDI template "All Parts" on the Genos (this automatically switches on transmitting and receiving of SysEx). And of course, the MD-BT01 adapter must of course be plugged in correctly (either to MIDI A In/Out or to MIDI B In/Out, observing the direction of the arrows for IN and OUT).
P.S.
Are you using the latest version (4.0.6) of Songbook+?
Best regards,
Chris