Okay, couple things.
Which ESXi -exactly-? Version and build number.
Are you running the vmxnet2 as Flexible?
Can you please retest with the 'legacy' interface? Preferably in pcn(4) mode over lnc(4) mode. I'm rusty so I forget how to force that behavior. (Hell, I forget if the PCIID changes were committed.)
How many em(4) (aka e1000) interfaces are you running during testing? Yes, this matters.
I think part of the problem is that 2.1 pulled in a bad em(4) branch - but I haven't had time to test more in depth.
EDIT: Oh, can you also please check to see if you have "calcru: runtime went backwards" messages?