Do you see any errors on the browser's developer console, in the Pegarules logs or the tomcat access logs? You can also run the fiddler and check what is preventing the loading of the components on the screen.
There are multiple things which can cause this but we will only know for sure once we have the data to analyse.
I have encountered similar issue. the loading just hangs there. This issue only affect one user. This particular user is doing development and there is some changes that he has done which cause the loading to go into loops.
I still has not find out the root cause, but all we did is just to reset this profile. i.e. change authentication mode and remove accessgroups. He is fine after we remove and put back his access. strange problem which we did not further investigate as the issue never occurs again.