After the case was escalated with Netapp, this was resolved.
Ended up being locks preventing giveback.
storage failover show-giveback
Partner
Node Aggregate Giveback Status
-------------- ----------------- ---------------------------------------------
<node>
CFO Aggregates Done
aggr2_sas_fas8020b
Failed: Operation was vetoed by
lock_manager. Giveback vetoed: Giveback
cannot proceed because non-continuously
available (non-CA) CIFS locks are present on
the volume. Gracefully close the CIFS
sessions over which non-CA locks are
established. Use the "vserver cifs session
file show -hosting-aggregate <aggregate
list> -continuously-available No" command to
view the open files that have CIFS sessions
with non-CA locks established. <aggregate
list> is the list of aggregates sent home as
a result of the giveback operation. If lock
state disruption for all existing non-CA
locks is acceptable, retry the giveback
operation by specifying "-override-vetoes
true". Warning: Overriding vetoes to
perform a giveback can be disruptive.
Once I overrode vetoes, the aggregate started rebuilding.
storage failover giveback -ofnode <node> -override-vetoes true