Acronis Backup: application-aware backup fails on newly installed SQL instance with "Account does not have enough privileges to access instance"

You have an application-aware backup of an SQL instance.

After a while, you add another SQL instance to your SQL server.

Backup completes with warning, second instance is not backed up:

2019-03-26T13:20:05:728+03:00 2236 W02140000: service_process(2976): Failed to save the metadata for group 'mssql://INSTANCETWO/DB_ONE'. Reason: 'Error 0x571102: Cannot back up SQL Server database 'DB_ONE' of instance 'INSTANCETWO'.
| line: 0xec865955c73bb297
| file: e:\301\enterprise\applications\mssql\aavb\addon\src\aavb_progress_control.cpp:62
| function: MsSql::AavbProgressControl::OnDatabaseError
| $module: aavb_mssql_backuper_vsa64_12420
|
| error 0x570133: Account '' does not have enough privileges to access instance 'INSTANCETWO'. To be able to back up or recover the instance, the account must have the SQL Server sysadmin role in it.
| line: 0xa590150b0bc6beec
| file: e:\301\enterprise\applications\mssql\common\src\online_mssql_server_information.cpp:1213
| function: `anonymous-namespace'::OnlineInformationBuilder::CollectMetaWithOdbc
| $module: aavb_mssql_backuper_vsa64_12420'.