I understand that I2C is on physical pins, but the equivalent position in Arduino digital/analog mapping IS dependent on the pin map.
If I used the mighty1284 standard map then the equivalent Arduino digital pins would NOT be D23 and D24, although the 1284P IC physical pins are obviously still 23 & 24.
You just said you were hoping from help from someone who has this working with the libraries in question. I do; a 1284P using several differently connected 8574, with both LiquidCrytal_I2C and Keypad_I2C, yet I'm offering 'useless advice'
If you don't want any input from someone with 'less than 1 years experience in MCU' then fine. The bottom line is that I2C works fine on my 1284p setup and not on yours, so go figure it out yourself without any further useless attempts from me to help.