Serial1.begin(9600,SERIAL_8N2) Crash ?!

[seeed xiao ble sense]
When I run the code below, ‘A’ gets printed, ‘B’ doesn’t, and the board crashes and I have to double-click to restart.
Does anyone know what the problem is?

void setup() 
{
    SerialUSB.begin(9600);
    while (!SerialUSB);

    SerialUSB.println("A");
    
    Serial1.begin(9600,SERIAL_8N2);
    while (!Serial1);
    
    SerialUSB.println("B");
  
}