I think we need a bit more extensive I/O logging here; so could you also try running
this "MonitorMIDI+OSC-IO.txt" script simultaneously with the StudioMix+REAPER.txt script, then post some results?
To prevent some duplicate messages, please also edit this line in the StudioMix+REAPER.txt script:
Code:
osc_log_input = 0; // (0 = OFF; 1 = ON)