I had this error appear too, but only because I skipped a step.  The rolling restart of the clustered search heads was critical after making the following server.conf change: [kvstore] storageEngineMigration=true  Once the rolling restart of the search heads completes, then enter the command: splunk start-shcluster-migration kvstore -storageEngine wiredTiger  The response should read "Starting KVStore Migration".  Check the migration status via: splunk show shcluster-kvmigration-status ... View more