I have an agregate with two CUs 6SL3054-0FC30-1BA0-Z F02

CU1 has 2 motors connected via drive-cliq hub 

and CU2 has 4 motors conected via another drive-cliq hub, like you can see at the picture below: 

From time to time CU2 went to stop without vissiable reason. 

After 24V restart I have only 1796 Wait for communication (3) error at all 4 drives.

As far as we assumed that it might be somehow  related to drive-cliq connection issue (like a bad connection or damaged cable or somthing..). But of course, we checked all plugs and cabeling for a few times and found no issue, Then  we tried to disconect drive-cliq cables one by one to simulate potentional failure and to check what will happen. 

An ineresting fact is that CU2 went to stop each and every time we conected back any drive-cliq hub  cable to it, while  CU1 does not. 

So the qestion is why CU2 went to stop and CU1 does not, at the same exect scenario of failure