The above message appears after cron finishes deleting entries created by a feed.
I import some users using /import/myfeed, then I delete the users using the Delete Items tab on the /import/myfeed/delete-items
50 users are deleted on each execution of cron and after the last batch this error appears.
In the job_schedule table the entry for feeds_source_clear still exists. I believe the issue is that the $job variable is set inside the then branch of the if statement in public function scheduleClear(), (FeedsSource.inc line 307) so that in the else branch where the job should be removed, the $job is undefined and thus not removed.