Timeout waiting for task in producer when moving shard leader

This happened [0] in a suite for module-based shards with tell-based protocol.

Karaf.log [1] shows an unexpected UnreachableMember at 06:17:00,808, followed by many warning as this:
2017-05-14 06:17:16,519 | WARN | ult-dispatcher-2 | FrontendClientMetadataBuilder | 199 - org.opendaylight.controller.sal-distributed-datastore - 1.5.0.Carbon | member-2-shard-default-config: Unknown history for commited transaction member-2-datastore-config-fe-0-chn-2-txn-2-0, ignoring

[0] https://logs.opendaylight.org/releng/jenkins092/controller-csit-3node-clustering-only-carbon/684/archives/log.html.gz#s1-s29-t1-k2-k9-k1
[1] https://logs.opendaylight.org/releng/jenkins092/controller-csit-3node-clustering-only-carbon/684/archives/odl2_karaf.log.gz