Our developers have taken a look at this issue, and our assets in the CAD's are usually just an object with our asset id which is an instance of some sort of re-usable component/definition/symbol that holds the placeholder geometry. This also means you can change those instances and those definitions.
They think what happened here is that either the reference to the definition or the definition itself got modified so that an empty object with just the asset id was left over. They would suggest the same action that I mentioned above to delete the asset from Enscape in such cases.
This isn't a bug but just how our asset system works.
Thanks for looking into this. I will try that solution.