I have 2 simple projects generated with Atmel Start, one is using external clock and the other is using internal clock. the I2C is working on the project with the internal clock and it doesn't work with the project with the external clock.
I'm using a custom board based on samd21j18a mcu, the board embeds an external oscillator, when using internal clock all used peripherals like (I2C, UART, RTC, WDG, GPIO) are working fine,
but when I use the external clock all peripherals keep working except the I2C which when debugging fail to write on the I2C bus.
The only difference between the 2 projects is the clock config in the config directory which I've attached bellow.