If you’re using the default Sky Sphere Blueprint we included, notice that you have to hit the “Refresh Material” checkbox to update the sky in the editor. That’s your giveaway - that means something needs to happen in order to update the sky.
If you open that Blueprint, you’ll see that there is a custom Function called UpdateSunDirection. Go into the Event Graph. Create an “Event Tick” node. Connect that to an UpdateSunDirection function call. You could put a delay on this for performance reasons, especially if your sun moves slowly (as it probably should). Now, if you animate your Light Source (make it moveable!!), the material sun will always move with it.
This is super fast to set up. Give it a try and let me know how it works.
EDIT: Oh, and before I forget, unless you use Delta Time from the tick to help control how much you rotate, then your sun will probably speed up and slow down based on hardware performance! You may or may not notice that depending on how fast the sun is moving, but it’s worth a mention.