I can confirm that along with the buzzer library, the QTRSensors library that comes as part of the Zumo library also has problems with the Arduino R4 WiFi.
After following the suggestion I made in the other thread I linked to (i.e. deleting the code in PololuBuzzer.cpp) the other functions of the Zumo library (i.e. motors, IMU, user pushbutton) seems to work fine though.
Brandon