airplay never sent initial probe for bonjour conformance test

I'm running airplaydemo and using bonjour confromance test(BCT) to capture the packets on an isolated Airport local network, however, BCT can never detect "initial probe from the device", i.e. no probe from airplay.

*** Please Power On Device ***

*** Beginning Link-Local Address Allocation Test ***
START (INITIAL PROBING)
WARNING 2023-10-10 11:42:39.997763-0500: Have not received initial probe from device.  Listening...
WARNING 2023-10-10 11:43:13.078729-0500: Have not received initial probe from device.  Listening...
WARNING 2023-10-10 11:43:45.105442-0500: Received address record query (name: devicex-000FFF0C527C.local., address: 169.254.65.124) before device successfully acquired a link-local IP address in subtest INITIAL PROBING.
WARNING 2023-10-10 11:44:15.374914-0500: Have not received initial probe from device.  Listening...
WARNING 2023-10-10 11:44:48.453606-0500: Have not received initial probe from device.  Listening...
WARNING 2023-10-10 11:45:21.611736-0500: Have not received initial probe from device.  Listening...
WARNING 2023-10-10 11:45:54.746021-0500: Have not received initial probe from device.  Listening...
WARNING 2023-10-10 11:46:27.786306-0500: Have not received initial probe from device.  Listening...
WARNING 2023-10-10 11:47:00.811269-0500: Have not received initial probe from device.  Listening...
WARNING 2023-10-10 11:47:33.855415-0500: Have not received initial probe from device.  Listening...
WARNING 2023-10-10 11:48:06.928281-0500: Have not received initial probe from device.  Listening...
ERROR   2023-10-10 11:48:06.928404-0500: *** Have not received initial probe from device. Giving up after 10 re-tries
FAILED (INITIAL PROBING)

However, airplay actually worked fine, I can play music to it, and it fails BCT due to the "initial probe".

Per my understand, "initial probe" here means "service announcement by airplay", but airplay never sends out that, instead, it responds to service queries from other devices(e.g. iphone, ipad) just fine, why is "initial probe" here a must have for BCT, why does not airplay send out them if it's a must-have for BCT?

Thanks for any helps or hints.