TAS6754-Q1: if DC load diagnostic can't detect Open Load, what should I check?

Part Number: TAS6754-Q1

Tool/software:

I have two TAS6754-Q1 on boards, their silicon version is 1p1. 

I tried to test open load on them by cutting off all the speakers.

The interesting result :

1) open load are detected on all the channels of first TAS6754-Q1 

2)open load are not detected on all the channels of second TAS6754-Q1 

Could you please tell me what should I check to get to know the reason?