Are you using the latest version of the exporter?
Are your faces oriented 'out' ? Use Monochrome view mode with a Style using a distinctive back-face material to check...
Can you post/PM the SKP of the glass for testing...
Here's a quick Octane Render I did of this SKP with [from left to right] smoothed, smoothed but reversed faces, NOT-smoothed [you can see the faceting ]. The latest versions of the Exporter work fine
[there
was a problem with the initial release which was ignoring smoothing etc but that's been fixed for a while]