The Output Pin Override Does not Function as Expected
When TWI is enabled, it overrides the output pin driver, but not the output value. The output on the line will always be high when the value in the PORTx.OUT register is ‘1’ for the pins corresponding to the SDA or SCL.
Work Around
Ensure that the values in the PORTx.OUT register corresponding to the SCL and SDA pins are ‘0’ before enabling the TWI.