Based on the information you provided, we think this might be the reason:
If the .dwg was exported from AC with an override and the translator has " Convert Objects to Blocks" checked, every single instance is saved with this naming convention: (nameoflibrarypart). If this is the case, let us know and we will look into it deeper and record it as a bug.
If after such an export the .dwg is imported to ARCHICAD with the "convert blocks to lib parts" option checked, naturally these will come in as individual lib parts.
Let us know, k