SSRS running report stuck on loading screen

I'm seeing a bizarre issue that is occurring daily when trying to run a report via the SSRS portal. Upon clicking the report, the entire screen grays out and pops up a Loading notification, which never advances. This is not the Loading message you get when running the report. The process never gets to the report screen (no report menu items, etc.). There are no errors in the log files, and the report execution is not attempted (nothing in the execution log in the ReportServer database for these reports). I've tried setting the recycle time to several days out then restarted the service, but the issue recurred the next day, even within less than the 12 hours of the default setting. The only thing that clears the issue is a restart of the Reporting Services service. This seems to work the rest of the day, but the following morning, ad hoc reports won't run. All scheduled reports are running successfully so this appears to be an issue with the portal. When this occurs, the same loading screen appears when trying to view subscriptions. All other functions on the portal seem to work.

This is occurring on all reports, including those with no parameters and which are not calling stored procedures.

Environment is as follows: 2 servers (1 RDBMS, 1 SSRS) SQL Server 2016 (13.0.4260 for SSRS) SQL Server 2016 (13.0.4466.4 for RDBMS) Windows Server 2012 R2

Try applying the latest Cumulative Update. You are on CU2, the latest is CU8. Until you can try that, schedule a Windows task to restart after hours in a window when no scheduled reports are running.