pic - Using internal pull-ups for I2C on PIC18F

I'm working with a PIC18F46J53 and it was working quite well without any troubles. Suddenly, I found a hindrance on my path.

I used RB4 and RB5 pins as I²C bus pins for communicating with an EEPROM (24LC256). And I pulled up the bus lines using external 10k on both SDA and SCL.

Whenever I initialize TRISB pins RB4 and RB5 as inputs a solid 3.2v will appear across them as I²C bus. But recently a problem popped up on my board: one pin, SCL, shows ~3.2V whereas SDA shows 0.8V - I²C,then, didn't work anymore. I cross checked the I/O pin configuration and when I enabled the internal pull-ups on the PORTB the voltage on SDA rose up to 2.0v and I²C worked fine with EEPROM.

From the datasheet:

RBPU: PORTB Pull-up Enable bit

1 = All PORTB pull-ups are disabled
0 = PORTB pull-ups are enabled by individual port latch values

To fix the problem I trust both pins SDA and SCL must have 2.8-3.2 V on the bus when configured as input. But it seems to be working with 2.0V on the SDA pin and 2.9V on SCL.

I would like your inputs to this problem if you have countered any difficulties like this before.

Where should I search to fix the problem? It's working for now but I trust I would have missed something in any case. When and how should one use pull-ups? I have used both external and internal in this case to get I²C working. What is the best way to do so?