Updated UE5 from 5.0.2 to 5.0.3, and the issue still occurs. Cutting/editing other grouped static and skeletal meshes work fine though, which is a bit bizarre since the Cube is the simplest static mesh there is. Any ideas? [unknown_2022.07.25-19.57]

Did you try it with a cube you made in modelling mode? ( rather than what looks like the engine cube )