We have a custom web application that uses SQL Server 2008 (10.50.1600). It's worked fine for years, but lately web pages that return data "instantaneously" have begun showing the "endless swirly blue thing" in IE. Something is causing queries to run slower, lock, contend or something else. Doesn't seem to be deadlocking, as I am not seeing deadlock errors at the user level, which I have (very rarely) seen (and know they will trigger a specific error).
If users close out of IE completely and go back in, they usually are able to do the previous work without this hanging behavior (well, until such time as the hang happens again).
How would you begin to diagnose the source of this issue?