Unexpected interruption of big project export

From #212355 (comment 368776276)

Problem statement

Big project export is getting interrupted before 6 hours job expiration mark https://gitlab.com/gitlab-org/gitlab/blob/master/app/workers/stuck_export_jobs_worker.rb#L15-15

All of the above happened before 6 hours mark. It has been interrupted twice before being marked as failed after 6 hours. Logs from #212355 (comment 368776276) expired and no longer available.

Expected behaviour

Project Export job should not be interrupted before 6 hours mark.

We need to investigate why this is happening and prevent exports jobs being interrupted.