You are right, the 4900M is a Catalyst, not Nexus model.
I have figured out a different solution in the meantime: enable flow control (switch side)/disable pause frames (NIC side, ethtool) when connecting 82599EB controllers to the 3064. I would even argue the ixgbe driver must have a long-standing bug with pause frame autonegotiation, but of course, IANAE.
