We recently migrated from a SQL Server 2008 SSRS server to a new SQL Server 2016. The entire report catalog was restored and upgraded to this new server. Everything is working, except the horrible performance of the web portal.
The performance while connecting to the web portal from a domain joined computer seems decent, but connecting to the web portal over the internet is seriously frustrating. Even simply trying to browse a directory of reports is a wait of several seconds, and running any given report is similarly slow. It's slow in IE11, Edge, Chrome, Safari, you name it. Like 25+ seconds to go from login to viewing the Home directory.
We are using NETWORK SERVICE as the service account, and NTLM authentication. We aren't getting any permission errors in the UI or the logs. HOWEVER in Edge browser, using the developer tools, I notice several 401 unauthorized HTTPS GET requests for things like reports/assets/css/app-x-x-x-bundle.min.css. So perhaps there is a permissions issue somewhere? Other interesting items in the developer tools is that things like reports/api/v1.0/CatalogItemByPath(path=@path)?@path= are taking like 10 seconds. These are JSON types.
Certain reports that do things like have a parameter depend on another parameter selection will sometimes not work. The waiting icon spins and when the report returns the selection will not be kept, nor the second parameter filled. Sometimes it works, however, which is part of what makes this so maddening.
There are no explicit error messages, but something is getting bogged down in a major way. There are no resource issues on this server that we can see- it's got plenty of headroom in terms of RAM and CPU.
This is not a report optimization problem; the entire UI is slow for everything.