The tests were done using T-SQL for the database and log backups.

All databases are in 'Full Recovery' mode.

The SQL Server Log does show this entry repeatedly:

BACKUP LOG WITH TRUNCATE_ONLY or WITH NO_LOG is deprecated. The simple recovery model should be used to automatically truncate the transaction log.

But I not see anything in the Maintenance plan that would indicate that the recovery modes are switched.

In addition further research has led me to run this query:

SELECT

DB_NAME(database_id), last_log_backup_lsn

FROM

sys.database_recovery_status;

This shows that the two problem databases have the last_log_backup_lsn = NULL

I gather this means the chain is broken and it has be restarted.

Would the correct procedure be:

1. Stop all user activity in the database

2. Switch to the SIMPLE recovery model (breaking the log backup chain and removing the requirement that the damaged portion of log must be backed up)

3.Switch to the FULL recovery model

4.Take a full database backup (thus starting a new log backup chain)

5.Start taking log backups