Symptom:
SF mode for BCM57810 works as expected, but when we change this to AFEX, we see very few packets increment on the interface, while the interface changes from vntag mode to down on the 5K.  We tried to get a span capture, but the span session never comes up, which I assume is due to almost no activity on the interface before it shuts down.

C220-M3 w/ 2.0(1a) firmware
[2] 5596 w/ 5.1(3)N2(1)

Conditions:
As soon as AFEX mode is enabled, the BCM57810 adapter stops sending frames, but SF mode works fine.