AX 2012 R3 SSRS - @SYS labels are shown in SSRS (Windows Server 2016 with SQL Server 2016) - Manually configured Reporting Extensions.

When you've configured SSRS or Reporting Extensions manually, there is a chance that you could not configure everything properly. There is such a situation when labels are not properly shown in SSRS reports.

This can be on one side caused by Service Account not matching with AOS account, which normally should be same and is called Proxy Account. But sometimes it can be caused be a setting, mentioned in 

C:\Program Files\Microsoft SQL Server\MSRS13.MSSQLSERVER\Reporting Services\ReportServer\rsreportserver.config file. 

The exact settting is as below, the tag or setting for RDCE should be enabled as True:

The below line:

<isrdceenabled>False</isrdceenabled>

Should look like as:

<isrdceenabled>True</isrdceenabled>

After changing it, you will need to restart SSRS service, and then run any SSRS report from AX 2012.