Hello,
When I have a site setup to use a Application Pool running ASP.NET v4 in Classic Mode, the first time I go to load a page, it will come up without issue. Subsequent requests for that same page will sit there and try to load forever. My testing is just loading an index.htm page with the word "Test" in it.
If I go ahead and recycle the Application Pool, it will work again for that first load, but fail after that.
I do not see anything of use in the Event Logs.