In the v1.8.9 release of the core the default ring buffer size was set to 256: https://github.com/arduino/ArduinoCore-samd/blob/1.8.9/cores/arduino/RingBuffer.h#L26-L32 After https://github.com/arduino/ArduinoCore-samd/pull/560 was merged it looks like this is reduced to 64 bytes now as `api/RingBuffer.h` is used instead of `RingBuffer.h` in [cores/arduino/SafeRingBuffer.h](https://github.com/arduino/ArduinoCore-samd/blob/master/cores/arduino/SafeRingBuffer.h): https://github.com/arduino/ArduinoCore-API/blob/master/api/RingBuffer.h#L33 This might also be related to https://github.com/arduino/ArduinoCore-samd/issues/644