How to send clock message from arduino to MIDI synth?

I'm trying to send periodically clock from arduino to Electron Digitakt synth with 120 bpm. It means I need to send 0xF8 every 21ms (60000/bpm/ppq -> ppq = 24 pulses per quarter)

My code looks like

void setup() 
{
  Serial.begin(31250);

  for (int i=0; i<10; i++) { Serial.write(byte(0xFF)); } // reset the slave
  
  Serial.write(byte(0xFA)); // send start command
  delay(10);

}

void loop () {
    Serial.write(byte(0xF8));
    delay(21);
}

But I see that my synth switches to Play but BPM doesn't change. I use logic analyser to check the output, it shows that this byte sends every 21ms (+- 1.2ms, usually a half of ms). Tried several libs for arduino with midi management, nothing helped

Could you help me to understand where is an issue?

Solution

From this MIDI tutorial for programmers it seems the Reset message should be used cautiously:

MIDI Reset message

This is a one status byte message 0xFF, without data bytes. It should reset the synthesizer to its power-on default, so it also stops all notes playing. Use this message sparingly, as it reset the full synthesizer, not only the notes playing.

I would suggest:

Sending only one reset message
Adding a delay after sending it. You will have to test an appropriate value