After jumping through the hoops of updating DPM2016 to UR2 to support the DPM SQL instance running SQL 2016, our SSRS broke.
Failed to load expression host assembly. Details: Could not load file or assembly ‘ReportSRV5, Version=1.0.523.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35’ or one of its dependencies. The system cannot find the file specified. (rsErrorLoadingExprHostAssembly)
Copy ReportSRV5.dll from old SSRS directory to new.
\Program Files\Microsoft SQL Server\MSRS12.MSSQLSERVER\Reporting Services\ReportServer\bin
\Program Files\Microsoft SQL Server\MSRS13.MSSQLSERVER\Reporting Services\ReportServer\bin\