When you remove all the other widgets, and make that the only widget in the blueprint does it render? if so then it would seem you can only have one 3D umg widget on a blueprint at a time would be my presumption, if not then your anchors are probably incorrect, if the anchors aren’t put in the right location, then elements become invisible, or more precisely what is being viewed is not the quadrant that the anchor is focusing on and hence is not in view.
hope that helps 