Arduino master to arduino slave code not working correctly

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so I've narrowed my problem down to an issue with trying to have the device have both master and slave capabilities. so i took a new approach, and now i can get it to work perfectly as either master or slave, but not both. i know you cant do both at the same time, but i had assumed you could switch between them, in an OR configuration. however, i am having issues with that.

Basically, this function on the slave:

void switchI2CMode(bool asMaster) {
  Wire.end(); // End current I2C operation to reconfigure
  
  if (asMaster) {
    // Configure as I2C master
    Wire.begin(); // Start I2C as master
 }
  
  else {
    // Configure as I2C slave
    Wire.begin(0x20); // join i2c bus with address 0x20 as a slave 
    Wire.onReceive(receiveEvent); // register event
    Wire.onRequest(requestEvent); // Register the onRequest event handler
  }
}

is supposed to select between master and slave mode. however Wire.onReceive(receiveEvent) & Wire.onRequest(requestEvent) only work when initialized in the setup routine, and once the device is switched into master mode, it ceased ever being able to function as a slave (until it is reset). does anyone know a workaround to this? microcontroller is a SAMD21G18A. Its on a custom board, so using a second sercom is not possible without a revised board.