Brian I had a similar issued with an object that was selected as a parttree part modified and then I used breakapart to convert it to an acis object, then the bounding box became visible with no object/part within. Thete was most likely other actions on this part/acis object that I performed, this happened about 2 weeks ago.
Honestly I cant remember how I got rid if the empty bounding box, but it did go away.
I suggest you attempt to verify what the original object was by getting all known entities separated and into a new drawing and then identify the likely culprit. Make a backup 1st.
If this is not feasible then can you selectively hide one object at a time via layers and confirm in hidden line render. Your attachent was deleted can you repost?
TCW V21, 2015-2020 PP, Animation Lab V5.2 & Redsdk enabled, LightWorks rendering mostly.