this is odd. Please check your network switch logs for errors (packet drops, flapping MAC addresses, etc.) as in general, SMB2 performance should be AT LEAST equal to SMB1 performance, in almost all cases even better.
Also, if you have a vif/ifgrp configured on your netapp, check that it matches the port config on the switch (i.e. link aggregate/etherchannel/trunk if your ifgrp is of type MULTI, and NO link aggregate if your ifgrp is of type SINGLE)