Import gets stuck reindexing while doing the Magic Potions after a successful import

Problem

When doing a JIRA Import, on the UI screen the reindex gets stuck for hours in the same reindex %. In the logs we see many:

... /secure/admin/StudioImport!import.jspa [atlassian.jira.index.AccumulatingResultBuilder] Indexing failed for Issue - '15519'
.../secure/admin/StudioImport!import.jspa [atlassian.jira.index.AccumulatingResultBuilder] java.nio.channels.ClosedByInterruptException

until it stucks there for hours.

This may not affect all imports.

Workaround

Contact Support who will restart the instance, do a full reindex and finish the import manually if it had attachments, logos and avatars.