August release - Failed to load expression host assembly

Thanks a lot for your patience and help to diagnose the issue

For your reference this is the entire assemblyBinding section for the two files in a clean install of PBIRS, after you udpate them you need to restart the service as some of you have mentioned and it should fix your issue.

"C:\Program Files\Microsoft Power BI Report Server\PBIRS\ReportServer\web.config"

    <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
      <dependentAssembly>
        <assemblyIdentity name="Microsoft.ReportingServices.Interfaces" publicKeyToken="89845dcd8080cc91" culture="neutral" />
        <bindingRedirect oldVersion="8.0.242.0-2018.8.0.0" newVersion="2018.8.0.0" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="Microsoft.ReportingServices.ProcessingCore" publicKeyToken="89845dcd8080cc91" culture="neutral" />
        <bindingRedirect oldVersion="9.0.242.0-2018.8.0.0" newVersion="2018.8.0.0" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="Microsoft.ReportingServices.ProcessingObjectModel" publicKeyToken="89845dcd8080cc91" culture="neutral" />
        <bindingRedirect oldVersion="9.0.242.0-2018.8.0.0" newVersion="2018.8.0.0" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="Microsoft.SqlServer.Types" publicKeyToken="89845dcd8080cc91" culture="neutral" />
        <bindingRedirect oldVersion="10.0.0.0-15.0.0.0" newVersion="14.0.0.0" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="msmgdsrv" publicKeyToken="89845dcd8080cc91" />
        <bindingRedirect oldVersion="9.0.0.0-15.0.0.0" newVersion="15.0.0.0" />
        <codeBase version="15.0.0.0" href="%ProgramFiles%\Microsoft Analysis Services\AS OLEDB\150\msmgdsrv.dll" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="Microsoft.Owin" publicKeyToken="31bf3856ad364e35" culture="neutral" />
        <bindingRedirect oldVersion="0.0.0.0-3.0.1.0" newVersion="3.0.1.0" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="System.Web.Cors" publicKeyToken="31bf3856ad364e35" culture="neutral" />
        <bindingRedirect oldVersion="0.0.0.0-5.0.0.0" newVersion="5.2.3.0" />
      </dependentAssembly>
    </assemblyBinding>

"C:\Program Files\Microsoft Power BI Report Server\PBIRS\ReportServer\bin\ReportingServicesService.exe.config"

    <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
      <probing privatePath="bin" />
      <dependentAssembly>
        <assemblyIdentity name="ReportingServicesAppDomainManager"
                          publicKeyToken="89845dcd8080cc91"
                          culture="neutral" />
        <bindingRedirect oldVersion="8.0.242.0-15.0.0.0"
                         newVersion="15.0.0.0" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="Microsoft.ReportingServices.Interfaces"
                          publicKeyToken="89845dcd8080cc91"
                          culture="neutral" />
        <bindingRedirect oldVersion="8.0.242.0-2018.8.0.0"
                         newVersion="2018.8.0.0" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="Microsoft.ReportingServices.Exceptions"
                          publicKeyToken="89845dcd8080cc91"
                          culture="neutral" />
        <bindingRedirect oldVersion="8.0.242.0-2018.8.0.0"
                         newVersion="2018.8.0.0" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="Microsoft.ReportingServices.ProcessingRenderingCommon"
                          publicKeyToken="89845dcd8080cc91"
                          culture="neutral" />
        <bindingRedirect oldVersion="8.0.242.0-2018.8.0.0"
                         newVersion="2018.8.0.0" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="Microsoft.ReportingServices.ProcessingCore"
                          publicKeyToken="89845dcd8080cc91"
                          culture="neutral" />
        <bindingRedirect oldVersion="9.0.242.0-2018.8.0.0"
                         newVersion="2018.8.0.0" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="Microsoft.ReportingServices.ProcessingObjectModel"
             publicKeyToken="89845dcd8080cc91"
             culture="neutral" />
        <bindingRedirect oldVersion="9.0.242.0-2018.8.0.0"
                         newVersion="2018.8.0.0" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="Microsoft.SqlServer.Types"
                          publicKeyToken="89845dcd8080cc91"
                          culture="neutral" />
        <bindingRedirect oldVersion="10.0.0.0-15.0.0.0" newVersion="14.0.0.0" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="Microsoft.Owin" publicKeyToken="31bf3856ad364e35" culture="neutral" />
        <bindingRedirect oldVersion="0.0.0.0-3.0.1.0" newVersion="3.0.1.0" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="System.Web.Cors" publicKeyToken="31bf3856ad364e35" culture="neutral" />
        <bindingRedirect oldVersion="0.0.0.0-5.0.0.0" newVersion="5.2.3.0" />
      </dependentAssembly>
    </assemblyBinding>

We will be working in a fix in order to solve the issues with the config files during the upgrade