In our DC we own couple of FEX'es with some Nexus'es 9k. The Nexus 9k doesnt support (or some versions of it) pre-provisioning with Fexes. Due to that i preconfigured port-channels and after we connected FEX'es - i added physical ports to already preconfigured Port-channels (VPC). Did the same for 6 (3x2) FEXes. 2 pairs of them worked fine, but all hosts on one particular pair FEX wasn't reachable - the ARP was alive. I tried everything from restarting the Fexes to debuging. The only thing that helped
was recabling and reconfiguring from scratch to new ports of Nexus 9k. I dont know why, but i think this have something to do with preconfiguration of port-channels.
Maybe you have some simmilar experience ? Or anyway to debug that.