Hey,
Translucent objects need to be set to a different z order so the system can know which one to render first. There are are two methods to sort z order in unreal. One is depth based, best suited for perspective camera and the other one is by z order. 0 is the furthest back and you add 1 as you come closer to the screen. You can find these in the settings tab under rendering.
P.s in the settings tab of a Sprite type ‘sort’ to find it and add the value there if you choose to use the second option.
Cheers.