[Quick Fix] Report Viewer not rendering controls correctly
While migration a legacy application to a new server environment we ran into the issue that the Report Viewer was not rendering its controls correctly. The Report Viewer was running on a webserver that was calling the reporting services on a SQL server within the same domain. Authentication was Kerberos, SPNs were properly defined and our reports were rendering, just the controls were having issues to apply the filters.
In the end the fix was easy, yet the root cause isn't quite clear (I can think of a few reasons, but none of them are at the moment substantially proven...)
Remove the SPNs, enable Kernel Mode authentication on the website that is rendering the report viewer and it will fix the issue.