During development of USB audio application, I have found bug in usb_device_audio.c of SDK v2.2.0.
Due to this bug all of audio class specific endpoint requests were rejected. That leads to ignore of
"SET SAMPLING FREQ CONTROL COMMAND", thus selection of sample frequency is not working.
To fix it remove lines 1553-1557 of usb_device_audio.c:
All bmRequestTypes already handled in switch and unsupported types will be ignored via default statement