That's a Revit limitation, not ARCHICAD. It may happen when you have smaller items, which are meshed (triangulated) upon export and end up as small triangles. Anything below a certain size is discarded by Revit.
Typical situations are inside the turns of a stair or within library objects with smaller details.
--- stefan boeykens --- bim-expert-architect-engineer-musician --- Archicad26/Revit2023/Rhino7/Unity/Solibri/Zoom MBP2023:14"M2MAX/Ventura+Win11 ARCHICAD-user since 1998 Archicad Book