I used the External System Import tool to import a bunch of new Stories with their sub-tasks into Jira. The importing tool didn't report any errors. I can see the stories correctly linked to the sub-tasks, and related to the existing Epics and other existing Stories. Basically, everything works as it should.
The issue is when I go to any board that includes the project I did the import for. Then, the board doesn't load.

I am assuming the culprit is the import because when I update the Board's filter to show me the issues before the import, then it works.
Filter: project = PROJECT_NAME AND created < 2017-10-14 ORDER BY Rank ASC
I tried to find the indexing tool, but I don't seem to find it under System.
Do you know how I can fix the issue? I am afraid that if I don't know what it is causing the error if I delete all the imported issues and load them again, the error will happen again.
Thanks!
Silvia