It could be because the bluetooth "protocol out" settings have been changed. The bluetooth module connects to the GNSS module by UART 2 port. baud rate is 38400 (bluetooth module baud rate has to be 38400). Please use U-center and update the UART2 port to the below values if they are not already with these values.
protocol in: RTCM3
protocol out: UBX+NMEA
baud rate: 38400
Form U-center menu, click View --> Configuration View (or the toolbar icon) and open the configuration view windows. Select UBX --> CFG --> PRT(Ports), Please refer to the below screenshot.
After changing the above settings, please save them permanently by following the below steps.