That's interesting because in this topic the export issue was marked as resolved: https://community.powerbi.com/t5/Report-Server/Export-data-to-Excel-not-working-in-Report-Server/td-...
If you open your browsers developer tools, can you see any errors when you try to do the export?
With the previous version issue you would see that it fails on trying get filesaver.min.js. I'm not getting that error anymore and it does the export for me successfully on the new version.
What happens for you?