[Koha] overdue_notives - to_address field is not populated

After upgrading to Koha 3.4.5 we have noticed that the overdue notices were not sent. The cron jobs are running and the message_queue table gets updated. The borrowernumber is correct in the message_queue but the to_address field is NULL. ( select email from borrowers where borrowernumber = xxx gives me the correct email) Any ideas why the to_address field is NULL and what to do about this? If I manually update the to_address and run process_message_queue.pl then the notices are sent ok. Thanks for any help. Rudy Wuthrich Kodaikanal International School