i2c working on one controller but not on another!

i am using nanos to communicate a parallel combination of 12 arduinos.I had checked the uno i2c behavior before converting it nto PCB but later on it doesnt work at all. It recieved a few data in the beginning but not after that. what could be poissiblr probem?

Please provide a wiring diagram of your setup.

You write you have 12 Arduinos on one I2C bus? How long is that bus? The maximal length of an I2C bus is about 1 meter but you shouldn’t use more than 0.5m of it if ever possible.

Did you test with one UNO and one Nano? And later on you added another ten Nanos? If my guesses are right you’ve chosen the wrong connection system. Use a bus that’s designed for such usages, probably best is RS-485 in your case.