If you have some features that look fine in the viewport, but they disappear or act weird when you hit play, or render with MRQ, then those actors might be on a sublevel that is set to the level blueprint streaming method.
You can check if you go to Window > Levels. See if Persistent level has any sublevels under it. If any have a blue dot next to the name, they are set to Level Blueprint Streaming. You can right click the level name in that menu, go to “Change Streaming Method” and set it to “Always Loaded”.
This is one possible reason this can happen.