GCS Warning 'No Data For xx seconds' occurred

Hi. I’m a beginner who has been using AP for less than a month. The first flight with AR WING900 was successful the other day, but the GCS data stopped updating when the CRSF link speed changed from 150 to 50Hz. I would like to know the cause. My configuration is:
FC: MATEK F405Wing
AP: V4.70
RX: TBS CRSF nano (FW6.xx: LATEST)
TX: LITE
CRSF WIFI (FW2.04)
Use Ch1 and 2 of CRSF nano for CRSF communication, set Ch3 and 4 to MAVLINK, connect to another UART from RC, and set to MAVLink2. GCS (AP) tablet connects to CRSF via UDP (port 8888). TBS AGENT WIFI connects to my iPhone hotspot.