the parsed RTCM packets are empty

[JeffYoung17]

Hello,
In the ntrip_ros.py
for raw_rtcm in self._client.recv_rtcm():

I'm sure that GPGGA data from GNSS is sent by ntrip client, and more than 400 bytes are read by ntrip clint as log print on the screen.
self._logdebug('Read {} bytes'.format(len(data))

But no RTCM32 preamble(0b11010011) is found in the rtcm_parser.py(I add log if header is matched, but there is no output), so the return value is empty
if combined_buffer[index] == _RTCM_3_2_PREAMBLE:

Could you give me some suggestions about how to debug? thank you