The control panel has some VERY stupid Javascript code where they decided to “optimize” the simple links and icons in the control panel main page with tens of thousands of lines of Javascript code. Because apparently showing a loading animation for multiple seconds is better than waiting for HTML code to be loaded in.
Some custom code in the control panel was changed recently which may have caused this issue. I’m going to investigate this and see if it can be improved.
EDIT: The custom code has been changed now so it should load a bit more efficiently. Due to caching and the like, it can still take a while for everything to work though.