Most imports require an existing REDengine file! For successful imports, ensure that the archive directory contains a "mirrored" file.
For example, both files below must be present for a successful mesh import:
Mod\base\characters\main_npc\judy\g1_001_wa_glove__judy.mesh
Raw\base\characters\main_npc\judy\g1_001_wa_glove__judy.glb