Convert Actors to Static Mesh doesn't work with Spline-/ and Instanced Static meshes

The Option “Convert Actors to Static Mesh” doesn’t work correctly with Actors that contain SplineMeshes and/or Instanced Static Meshes

Here, the Railing is a Spline Mesh and the Balusters are Instanced Static Meshes

However, After “Convert Actors To static Mesh” it looks like this:

Hey Raildex_,

Thanks for reporting this. I’ve entered UE-44904. You can track the report’s status as the issue is reviewed by our development staff. Please be aware that this issue may not be prioritized or fixed soon.

Use the Merge Tool.

Link to a similar Topic: Convert spline actor to static mesh strange result - Blueprint - Epic Developer Community Forums

See this solution from Unreal as it mught help you, Its called actor merging: Paragon Feature Examples: Foliage & Parallax Occlusion Mapping | Feature Highlight | Unreal Engine - YouTube also see this thread:
Convert spline actor to static mesh strange result - Blueprint - Unreal Engine Forums