MCT8315A: No replies of MCT when 3.3V is delayed !!!

Tool/software:

Hi,

I use a MTC8315AIV on a custom board, and I have an issue about I2C (no response of MCT).
I make a long time to isolate the problem, but now I have only one parameter (+3.3V voltage to delayed, see description below) to reproduce it.

The hardware context on my custom board : 
The input voltage (VM=+7V) is connected to VM pins (9, 10 and 11) of MCT8315.
An internal voltage +3.3V is generated by other component (DC/DC converter) and appears 800ms after VM. This 3.3V voltage is used (with pull-up resistors) on SDA, SCL, FG and FAULT pins of MCT8315.

The hardware context with EVM board to reproduce/investigate it : 
I disconnect the MCT of my custom board (remove serial resictor on I2C bus) and I connect an EVM MCT8316 (Brushless 25 Click board) :GND, SDA and SCL signals.

Case 1 : To reproduce the same issue I2C as my custom board), I connect the 3.3V from my board (800ms of delayed) to EVM board input 3.3V and launch a I2C scan --> the MCT chip doesn't repond

Case 2 : I take the 3.3V voltage from AVDD MCT (pin 27) and connect it to EVM board input 3.3V, and launch a I2C scan --> The MCT chip replies to the I2C scan

Do you have an explanation of this behaviour ? With the 3.3V delayed, is the MCT in sleep mode (I2C disabled) ? if yes, how to exit ?

note : I can't use the AVDD signal from MCT to pull up the I2C, FG and Fault signals because the PCB is already done.

Thank to advance

Eric