Check this point from cisco "red text"
Should I enable vPC auto-recovery?
It is a good practice to enable auto-recovery in your vPC environment.
There is a slight chance that the vPC auto-recovery feature might create a dual-active scenario. For example, if you first lost the peer-link and then you lost the peer-keepalive, you will have dual-active scenario.
In this situation, each vPC member port continues to advertise the same Link Aggregation Control Protocol ID that it did before the dual-active failure.
A vPC topology intrinsically protects from loops in case of dual-active scenarios. In a worst case scenario, there are duplicate frames. Despite this, as a loop-prevention mechanism, each switch forwards Bridge Protocol Data Units (BPDUs) with the same BPDU Bridge ID as prior to the vPC dual-active failure.
While not intuitive, it is still possible and desirable to continue to forward traffic from the access layer to the aggregation layer without drops for current traffic flows, provided that the Address Resolution Protocol (ARP) tables are already populated on both Cisco Nexus 7000 Series peers for all needed hosts.
If new MAC addresses need to be learned by the ARP table, issues might arise. The issues arise because the ARP response from the server might be hashed to one Cisco Nexus 7000 Series device and not to the other, which makes it impossible for the traffic to flow correctly.
Suppose, however, that before the failure in the situation just described, traffic was equally distributed to both Cisco Nexus 7000 Series devices by a correct PortChannel and by an Equal Cost Multipath (ECMP) configuration. In this case, server-to-server and client-to-server traffic continues with the caveat that single-attached hosts connected directly to the Cisco Nexus 7000 Series will not be able to communicate (for the lack of the peer link). Also, new MAC addresses learned on one Cisco Nexus 7000 Series cannot be learned on the peer, because this would cause the return traffic that arrives on the peer Cisco Nexus 7000 Series device to flood.
