I have exactly the same problem, using both Firefox and Safari on MacOS. The dialog recognizes the file that I uploaded, but when I click "save" it complains that I haven't slected a route to save, even though I have.
The other problem I have is that none of my Pocket Queries that I generated have been emailed to me. I can preview them, but I never get sent the GPX file with results.
So, basically, the features I paid to be a premium member to use, don't work.