For the past few weeks I have tried to use the Great Vault upgrade finder but no matter how I import my character (GV open, GV generated but closed, etc) the upgrade finder says it can’t see anything in the vault.
You do need to open up your great vault to see the potential rewards once before we can read them. Once you can see the rewards yourself, going to the Export tab of the in-game addon should be able to read them, even if the great vault window is subsequently closed.
After exporting your character from the addon to the website, could you press the “help” link next to the big Upgrade Finder section header, then press “Create Support Post” to generate a snapshot ID, and copy it here? With that I can see whether it is not reading anything from the game or something else is happening.