Custom Blueprint SceneComponent added to object in level, component disappears after recompile

I want to create a reusable blueprint component which can be added to already existing actors in the level.
This is working if I create a fresh blueprint inherited from SceneComponent. But once I add a variable to it and klick recompile (on the component or the main blueprint) it will get deleted from the level.

If I add this component directly to an Actor Blueprint and place this Blueprint in a level, all the changes I make to its component properties are ignored.

Not sure if this functionality is intended but this makes blueprint components useless for setting up things in the level.

The image shows two components which are supposed to decorate a spline. The red component disappears after recompile. The blue one is directly set in the blueprint and should actually show the cone mesh, but it doesn’t.