I have tried to further isolate my experience.
I have a simple solid with a half sphere and a ring below it.
I am pretty sure it is all solid, and these two parts are "Body1" and "Body2" in the subfolder of bodies in the main tree, but on exporting to .stl, I only get the ring component.
I would attach the .dwg here, but cannot work out how to specifically save the .dwg locally yet, its stuck in the cloud right now :-(
did a join between the two parts, and then the export to stl has the full component.
I am pretty sure this is a kludge, but at least I have a way forward...
We made changes to the access point due to a change in the dashboard. If you select the three bars on the left side you will see various options. One of the options is to Export Archive.