Hi, If you have them stacked you don’t need a port channel between the two switches, either have a LAG or a stack, not both.   
I've got (2) N4032's in a 40GB stacked configuration using the 2 port QSFP cards in each.  I'm connecting port 1/1/1 to port 2/1/2 and 1/1/2 to 2/1/1 respectively.  The units stack successfully, but when I configure the LAG / port-channel and then status them...the Port-channel is showing as INACTIVE.  I don't have any traffic between the switches yet so I'm wondering if this may be the cause.[IMAGE]
N4032 QSFP ports in a LAG