Use Group Managed Service Account for SSRS
Try removing the managed service account like so by running the following command on your local SQL/SSRS Server:

Remove-ADComputerServiceAccount -Identity [Your Server Name] -ServiceAccount domain\SSRSProdSvc$


https://technet.microsoft.com/en-us/library/dd378979(v=ws.10).aspx

And if this hasn't been done, add the new managed account to the local server:


  
  On the domain controller, click Start, and then click Run. In the Open box, type dsa.msc, and then click OK to open the Active Directory Users and Computers snap-in. Confirm that the Managed Service Account container exists.
  Click Start, click All Programs, click Windows PowerShell 2.0, and then click the Windows PowerShell icon.
  Run the following command: New-ADServiceAccount [-SAMAccountName ] [-Path ].
  Associate the new MSA to the computer account by running the following command: Add-ADComputerServiceAccount [-Identity] &lt;ADComputer&gt; &lt;ADServiceAccount[]&gt;
  
  See Add-ADComputerServiceAccount for the complete syntax.
  


per Microsoft:
https://technet.microsoft.com/en-us/library/dd548356(v=ws.10).aspx