I2C question on arduino Due?

using pins 20 and 21 with 5V(on board) and 10k pullup. no external power. IT is used to drive AtTiny 4313 and ADS1115. It works. once in a while. it does not. suggest if this setup is right Thanks, yuva

I can't tell from here but it seems like maybe you've got a 5V pullup on a 3.3V pin? That's a bad idea.