I still think these two posts are the most likely avenue for troubleshooting:
In the second of these, “It would be interesting to see both the OSC timestamps of the outgoing bundles on the client and the OSC timestamp for each audio callback on the server. Then we could see if there’s a problem with one particular clock. However, for that we would need to insert some printf statements.”
That is, insert some print statements into the C++ sources and rebuild for testing. Perhaps later I could suggest the print statements, but I’m not on Mac so I couldn’t build it for you.
hjh