I2C - Sometime the slave response but most of time not


I am trying to communicate with a slave device, sometimes the slave response and everything is working without a problem.

But most of the time the slave device is not responding to the "first acquire" (first i2C communication done after a reset or reprogramming the uC) with an ack.

I don't thing that it is a code issue, because if it was I wouldn't expect it to work at all. but I am running out of ideas as I disconnect all the other component from the board and left only the I2C slave connect the uC.

Any advice?

Please, post your codes with code tags </> along with the Arduino types you are using as Master and Slave.