TLK3132: TBI is not working

In my design I use the TLK3132 device and I have the following situation:

I have external H/W loop and the Self Test is working properly.

Then I de-activate the internal Self Test and I send a specific pattern at the TxD inputs (TBI mode).

At RxD I don't receive this specific pattern but instead I receive random data.

Could you indicate some possible issues that could lead to this behavior?