Hello,
are you still looking for some input on this?
If yes,
I had experienced this type of problems. And, for all Microsoft NLB applications, We had to create networks on legacy network devices only.
As per my discussions with one of the Microsoft teams, They had no plans to change the MAC address ( Non-RFC standard) to support SDN technologies like ACI
We tried all possible ways like flooding enabled, gateway outside of ACI fabric --still, there is an intermittent disconnections.
it is best not to connect these servers to Cisco ACI.