I'm sorry to hear that some of your users are running into an issue loading apps on IE and Edge. Is it possible for your users to provide us with some session IDs?
They should be able to get them from the loading screen by holding down Alt and right-clicking on the loading screen. This should bring up a small context menu with a button labelled "Session details" that they can click. After they click on that button, their session ID will be displayed. That information can help us track down what's causing your users' apps not to load.