Version 8.0 Situation - sending monthly campaign of about 1000 emails. Problem - often, a few (usually less than 10) emails are 'hung' in limbo, the campaign does not finish. The x2_list_items.sent = 0 and x2_list_items.sending = 1 for these records. Typical Error.log entry - 2021/02/02 00:01:59 [error] [exception.CDbException] CDbException: CDbCommand failed to execute the SQL statement: SQLSTATE[40001]: Serialization failure: 1213 Deadlock found when trying to get lock; try restarting transaction - UPDATE x2_list_items AS i LEFT JOIN x2_contacts AS c ON c.id=i.contactId SET i.sent=:sent,i.un