CSIT Sporadic failures - missing table=21 rule for VM private IP

Rule for 90.0.0.8 is missing in the NAPT switch

https://logs.opendaylight.org/releng/jenkins092/netvirt-csit-1node-openstack-newton-upstream-transparent-carbon/432/archives/log.html.gz#s1-s1-s3-t19

There is a missing 90.0.0.8 flow in OS_COMPUTE_2 (which is the NAPT switch, and therefore it is required for the SNAT test to pass). Looking at the logs, there is a FIB DjC failure for this IP (see below) - I think this might be the root cause (even though the exception is for a different dpnId, I believe this somehow relates to the missing flow).
I couldn't find what scenarios are making those conflicting modifications.

2017-03-22 20:33:50,664 | WARN | lt-dispatcher-16 | ShardDataTree | 218 - org.opendaylight.controller.sal-distributed-datastore - 1.5.0.SNAPSHOT | member-1-shard-inventory-config: Store Tx member-1-datastore-config-fe-0-txn-19006-0: Conflicting modification for path /(urn:opendaylight:inventory?revision=2013-08-19)nodes/node/node[

{(urn:opendaylight:inventory?revision=2013-08-19)id=openflow:31692983464182}

]/AugmentationIdentifier

{childNames=[(urn:opendaylight:flow:inventory?revision=2013-08-19)port-number, (urn:opendaylight:flow:inventory?revision=2013-08-19)stale-group, (urn:opendaylight:flow:inventory?revision=2013-08-19)supported-match-types, (urn:opendaylight:flow:inventory?revision=2013-08-19)table, (urn:opendaylight:flow:inventory?revision=2013-08-19)group, (urn:opendaylight:flow:inventory?revision=2013-08-19)manufacturer, (urn:opendaylight:flow:inventory?revision=2013-08-19)software, (urn:opendaylight:flow:inventory?revision=2013-08-19)ip-address, (u rn:opendaylight:flow:inventory?revision=2013-08-19)serial-number, (urn:opendaylight:flow:inventory?revision=2013-08-19)table-features, (urn:opendaylight:flow:inventory?revision=2013-08-19)supported-actions, (urn:opendaylight:flow:inventory?revision=2013-08-19)hardware, (urn:opendaylight:flow:inventory?revision=2013-08-19)description, (urn:opendaylight:flow:inventory?revision=2013-08-19)switch-features, (urn:opendaylight:flow:inventory?revision=2013-08-19)supported-instructions, (urn:opendaylight:flow:inventory?revision=2013-08-19)stale-meter, (urn:opendaylight:flow:inventory?revision=2013-08-19)meter]}

/(urn:opendaylight:flow:inventory?revision=2013-08-19)table/table[

{(urn:opendaylight:flow:inventory?revision=2013-08-19)id=21}

]/flow/flow[

{(urn:opendaylight:flow:inventory?revision=2013-08-19)id=L3.31692983464182.21.3d874586-2408-4a13-b4c6-6ef01747cd34.42.90.0.0.8}

].
2017-03-22 20:33:50,664 | ERROR | ult-dispatcher-5 | LocalThreePhaseCommitCohort | 218 - org.opendaylight.controller.sal-distributed-datastore - 1.5.0.SNAPSHOT | Failed to prepare transaction member-1-datastore-config-fe-0-txn-19006-0 on backend
OptimisticLockFailedException

{message=Optimistic lock failed., errorList=[RpcError [message=Optimistic lock failed., severity=ERROR, errorType=APPLICATION, tag=resource-denied, applicationTag=null, info=null, cause=org.opendaylight.yangtools.yang.data.api.schema.tree.ConflictingModificationAppliedException: Node was created by other transaction.]]}