Timeout on I2C Write BUSY - not all the time [Adafruit 8x8 matrix backpack]

Hello,
i'm working with a pico and an Adafruit 8x8 matrix backpack (HT16k33).
I setup the I2C and initialize the display

  I2C1.setup({scl: B6,sda: B7});
  I2C1.writeTo(0x70, 0x21); // turn on oscillator
  I2C1.writeTo(0x70, 0x81); // display on

Some time (i'm unable to find a recurrent way, it come on a software upload or a switch on) the display does not start, with an I2C timeout (in the console)...
I've tried with decay for writing command..
same prob.

I2C1.setup({scl: B6,sda: B7});
  setTimeout(function() {
    I2C1.writeTo(0x70, 0x21); // turn on oscillator
    I2C1.writeTo(0x70, 0x81); // display on
  }, 500);

Any idea?
It is not a wiring pb (cause most of the time it work)

thanks for yopur help