Blueprint viewport empty despite full of components

You can see their transform manipulators, you can see debug lines like a spring arm length or spline when that component is selected (invisible otherwise), all meshes are invisible, there are no destruction nodes, all component visibility is on, if I pull the BP into a level the eye is already turned off in the world outliner and will not switch on unless show selected at startup is toggled, this has never happened to me in 6 engine versions.

I’ve trawled google for a few weeks now, people with empty viewports either destroyed their actor or needed to refocus the viewport camera, but those aren’t the problem here unfortunately. Help?