Fixes: #3765 - Possible race condition causing OTRS import to fail

db/migrate/20210923075329_remove_otrs_diff_worker_scheduler_entry.rb

@@ -0,0 +1,10 @@
+# Copyright (C) 2012-2021 Zammad Foundation, http://zammad-foundation.org/
+
+class RemoveOtrsDiffWorkerSchedulerEntry < ActiveRecord::Migration[6.0]
+  def change
+    # return if it's a new setup
+    return if !Setting.exists?(name: 'system_init_done')
+
+    Scheduler.find_by(method: 'Import::OTRS.diff_worker')&.destroy
+  end
+end

db/seeds/schedulers.rb

@@ -21,15 +21,6 @@ Scheduler.create_if_not_exists(
   prio:   1,
   active: true,
 )
-Scheduler.create_if_not_exists(
-  name:          'Import OTRS diff load',
-  method:        'Import::OTRS.diff_worker',
-  period:        3.minutes,
-  prio:          1,
-  active:        true,
-  updated_by_id: 1,
-  created_by_id: 1,
-)
 Scheduler.create_if_not_exists(
   name:          'Check Channels',
   method:        'Channel.fetch',