Pivotal Tracker import - Unexpected failure occurred. Importer will stop immediately.

[Daniel Becroft]

Environment: JIRA Server 7.3.0

We have successfully migrated all but 1 of our projects from Pivotal Tracker into JIRA, and have been running successfully for about 6 weeks. We are now trying to import the final project across, but we are getting the following error:

2017-05-18 17:19:29,912 INFO - Import started by pivotal-tracker using com.atlassian.jira.plugins.importer.imports.pivotal.PivotalDataBean
2017-05-18 17:19:29,912 INFO - ------------------------------
2017-05-18 17:19:29,912 INFO - Importing: Users
2017-05-18 17:19:29,912 INFO - ------------------------------
2017-05-18 17:19:29,912 INFO - Only new items will be imported
2017-05-18 17:19:31,177 INFO - 28 users associated with import. All of them imported as inactive, this can be changed after import in User Access step.
2017-05-18 17:19:31,177 INFO - ------------------------------
2017-05-18 17:19:31,177 INFO - Finished Importing : Users
2017-05-18 17:19:31,177 INFO - ------------------------------
2017-05-18 17:19:31,177 INFO - 0 users successfully created.
2017-05-18 17:19:31,177 INFO - Retrieving projects...
2017-05-18 17:19:31,177 INFO - Project ExternalProject{id='866977', key='SBPA', externalName='Support Backlog', name='Support Backlog (Pivotal Archive)'} exists and found correctly.
2017-05-18 17:19:31,240 ERROR - Unexpected failure occurred. Importer will stop immediately. Data may be in an unstable state
java.lang.RuntimeException: Error setting up Pivotal Rapid Board for project SBPA
	at com.atlassian.jira.plugins.importer.imports.pivotal.PivotalDataBean$3.afterProjectCreated(PivotalDataBean.java:359)
	at com.atlassian.jira.plugins.importer.imports.importer.impl.DefaultJiraDataImporter.importProject(DefaultJiraDataImporter.java:668)
	at com.atlassian.jira.plugins.importer.imports.importer.impl.DefaultJiraDataImporter.doImport(DefaultJiraDataImporter.java:369)
	at com.atlassian.jira.plugins.importer.imports.importer.impl.ImporterCallable.call(ImporterCallable.java:26)
	at com.atlassian.jira.plugins.importer.imports.importer.impl.ImporterCallable.call(ImporterCallable.java:15)
	at com.atlassian.jira.task.TaskManagerImpl$TaskCallableDecorator.call(TaskManagerImpl.java:458)
	at com.atlassian.jira.task.TaskManagerImpl$TaskCallableDecorator.call(TaskManagerImpl.java:426)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at com.atlassian.jira.task.ForkedThreadExecutor$ForkedRunnableDecorator.run(ForkedThreadExecutor.java:216)
	at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.NullPointerException
	at com.atlassian.jira.plugins.importer.appbridge.software.JimJiraSoftwareAccessorImpl.createRapidBoard(JimJiraSoftwareAccessorImpl.java:131)
	at com.atlassian.jira.plugins.importer.imports.pivotal.PivotalDataBean$3.afterProjectCreated(PivotalDataBean.java:354)
	... 11 more
2017-05-18 17:19:31,240 INFO - No issues need to be reindexed.

This seems to have been asked previously[1], but the accepted answer was that it was an issue in the 7.0 release line (we have always been on 7.3).

We have tried renaming the PT Workflows and issue statuses that get created, but to no avail. Is there anything else that we can look at to resolve?

[1] - https://community.atlassian.com/t5/JIRA-Core-questions/Unexpected-failure-occurred-Importer-will-stop-immediately-Data/qaq-p/310963