Hi @Harshada -
Extending the cables is definitely responsible for your issues - but not due to voltage drop. I2C is a protocl that was never intended to run for long ditances, so any extension beyond the default cable length is liable to run into trouble, especially in a noisy electrical environment like an ROV.
This guide has some tips for extreme lengths, but generally the best course of action is to examine your clock and data lines with an oscilloscope, and add a Resistor/Capacitor filter to help make sure you have nice square transitions on your signals. Lowering the frequency of the I2C bus can also help, and won’t affect much given the low data rates involved.