On an attempt to make custom stylized water, I created a “Water rectangle” (name in outliner) and added the custom stylized material that I made.
Due to the material being “translucent” I couldn’t select it anymore on the viewport, but I could always search for its name and grab it from the outliner.
However, after restarting UEFN, I could no longer find the actor in the outliner, even though it exists in the level, and I cannot remove or edit it anymore.