Thanks @HughesTooling
There are two known issues that affect this workflow. The most common is fixed by a clean uninstall, using the cleaner tool or manual steps. There is also a workaround.
https://knowledge.autodesk.com/support/fusion-360/troubleshooting/caas/sfdcarticles/sfdcarticles/Fus...
Workaround: Export the STL files from a web browser instead of the Fusion 360 desktop client.
The less common issue is related to network shares. If the last used export location is a network share that is not available Fusion will crash.
Here is a customer comment about it.
"...it was the network share shortcut in file save dialog that was connected to password protected network share. Fusion 360 never asked for any credentials and it just .. failed. After clicking on the share with Explorer and entering credentials Fusion 360 started working again."
Here is another forum report with similar outcome:
https://forums.autodesk.com/t5/fusion-360-support/creash-on-stl-export-to-bit-locked-drive/m-p/84828...
Please let me know if either of these are happening for you.
Phil Eichmiller
Software Engineer
Quality Assurance
Autodesk, Inc.