Avamar: SQL differential backup completes with the exception "Couldn't find the differential_base_lsn value in the metadata file"

The Avamar SQL plug-in backup log presents the following lines for the differential backup.

2018-06-06 11:13:39 avsql Warning <17378>: Private properties of resouce could not be resolved for Name.
2018-06-06 11:13:45 avsql Warning <43543>: Couldn't find the differential_base_lsn value in the metadata file. 
Due to the changes in this plugin version, it is recommended to take a FULL backup for the database '<sql-db-name>'.

The above warning showed up because Plugin backup left "Differential_base_lsn" values as empty when different logical names are detected for the same database. To check Logical Names" run SQL query:

SELECT d.name AS DatabaseName,
       f.name AS LogicalName,
       f.physical_name AS PhysicalName,
       f.type_desc AS TypeofFile
FROM sys.master_files f
INNER JOIN sys.databases d ON d.database_id = f.database_id;

Here are the results:

DatabaseName	LogicalName	PhysicalName	TypeofFile
master		master	C:\Program Files\Microsoft SQL Server\MSSQL13.MSSQLSERVER\MSSQL\DATA\master.mdf	ROWS
master		mastlog	C:\Program Files\Microsoft SQL Server\MSSQL13.MSSQLSERVER\MSSQL\DATA\mastlog.ldf	LOG
tempdb		tempdev	C:\Program Files\Microsoft SQL Server\MSSQL13.MSSQLSERVER\MSSQL\DATA\tempdb.mdf	ROWS
tempdb		templog	C:\Program Files\Microsoft SQL Server\MSSQL13.MSSQLSERVER\MSSQL\DATA\templog.ldf	LOG
model		modeldev	C:\Program Files\Microsoft SQL Server\MSSQL13.MSSQLSERVER\MSSQL\DATA\model.mdf	ROWS
model		modellog	C:\Program Files\Microsoft SQL Server\MSSQL13.MSSQLSERVER\MSSQL\DATA\modellog.ldf	LOG
msdb		MSDBData	C:\Program Files\Microsoft SQL Server\MSSQL13.MSSQLSERVER\MSSQL\DATA\MSDBData.mdf	ROWS
msdb		MSDBLog	C:\Program Files\Microsoft SQL Server\MSSQL13.MSSQLSERVER\MSSQL\DATA\MSDBLog.ldf	LOG
db_1		DB_1	C:\SQL_AG_2\DB_1.mdf	ROWS
db_1		DB_1_log	C:\SQL_AG_2\DB_1_log.ldf	LOG
db1_2020	DB_1	C:\Recovery\db1_2020_data_0.mdf	ROWS
db1_2020	DB_1_log	C:\Recovery\db1_2020_log_0.ldf	LOG
feb13_restore	DB_1	C:\SQL_AG_2\feb13_restore_data_0.mdf	ROWS
feb13_restore	DB_1_log	C:\SQL_AG_2\feb13_restore_log_0.ldf	LOG
db_1_1		DB_1	C:\Program Files\Microsoft SQL Server\MSSQL13.MSSQLSERVER\MSSQL\file	ROWS

"Differential_base_lsn" values are empty when different logical names are present for a database.
The above warning message causes the backup to complete with an exception, but the backup is valid and can be restored fully. The issue was addressed with the change in the Plugin code to not rely on Database logical names.

The warning can be safely ignored.
Alternatively contact Avamar support for a Plugin hotfix where the cosmetic issue has been fully addressed.