Ugh. Sorry. In my effort to streamline the 'bug,' I ended up going back too far, and I believe you are right, I did not select it before exporting.

In anycase, HERE is the file which won't export-- even when selected.
https://altuit.cloud/web/dbpub/3D/bugExport2.3dm

As you can see in the image below, it hangs at 15% and never gets any farther. fyi, I'm on Mac with latest version of El Capitain



Also, FWIW, I've tried several different export settings with none of them working.