In SQL Management Studio, the SQL Model DB does not show a last backup timestamp after an log truncation job is performed.
The model database is the template used by Microsoft SQL Server when you create a user database. The entire contents of the model database, including database options, are copied to new databases when created. Some of the settings of model are also used for creating a new tempdb during start up, so the model database must always exist on a SQL Server system.
Newly created user databases use the same recovery model as the model database. The default is user configurable. To learn the current recovery model of the model, see How to: View or Change the Recovery Model of a Database (SQL Server Management Studio).
When the Appassure 5 or Rapid Recovery 6 Full backup is performed, the snapshot will include all DBs present on the system but the Model DB will not reflect the backup timestamp. Neither Appassure 5 or Rapid Recovery 6 will report to VSS / SQL that the Model DB was backed up because this is a System Database that is used as a template and it is not a live user created database.
This is normal behavior and does not indicate there is an issue with the backup or the recovery point / data within the recovery point. Our products perform volume / block level backups so all data that exists on a protected disk is being included in the snapshot / recovery point. SQL queries for last backup will not reflect that our agent has actually performed a backup of the Model DB but if you were to mount a recovery point for the volume that includes the Model DB location you should be able to manually navigate and locate it in the recovery point.
The only time that the Model DB stats and metrics would change is after a native SQL job is performed or the SQL DBA has manually made a change which will then be reflected in new databases created thereafter.