Fix a really rare race condition in the migration scheduler. (#9000)

migrations/scheduler.go

@@ -59,7 +59,7 @@ func (scheduler *Scheduler) ScheduleJob(cfg *model.Config, pendingJobs bool, las
 
 		if state == MIGRATION_STATE_IN_PROGRESS {
 			// Check the migration job isn't wedged.
-			if job != nil && job.LastActivityAt < model.GetMillis()-MIGRATION_JOB_WEDGED_TIMEOUT_MILLISECONDS {
+			if job != nil && job.LastActivityAt < model.GetMillis()-MIGRATION_JOB_WEDGED_TIMEOUT_MILLISECONDS && job.CreateAt < model.GetMillis()-MIGRATION_JOB_WEDGED_TIMEOUT_MILLISECONDS {
 				mlog.Warn("Job appears to be wedged. Rescheduling another instance.", mlog.String("scheduler", scheduler.Name()), mlog.String("wedged_job_id", job.Id), mlog.String("migration_key", key))
 				if err := scheduler.App.Jobs.SetJobError(job, nil); err != nil {
 					mlog.Error("Worker: Failed to set job error", mlog.String("scheduler", scheduler.Name()), mlog.String("job_id", job.Id), mlog.String("error", err.Error()))