UE5 is showing performance issues with UI as far as materials responding to value changes you make, especially scalar parameters. If you adjust a material, say in a Material Instance, you sometimes get no response, so you think that there is a BP coding issue, but then you move around the UI and then the change kicks in later. This is very problematic to work through.
Also, sliders for scalar parameters, when they do work more immediately, are sluggish. The change is not visible in realtime like it was in say 4.26, 4.27. So you have to wait until it lags a few seconds, and then it resolves the change you made and shows the result.