Folks, I finally managed to get an update to my UWP app into the store. As I said, I spent hours wandering around the portal, help pages and samples, but none of the process seemed to match the descriptions. I eventually noticed a little *support* link and emailed a question about the state of the app and how it could be updated. A week later, the following sentence from the response offers a clue about what was wrong.
*We have enabled the ability to update your app, and it may take up to 24 hours before Partner Center is ready to accept updates. Please submit an update to the app and ensure that it has an active presence in the Store, or it may be unpublished again.* So they "enabled" the app again. I guess from this, that the app was in some unrecognisable "state" which disabled the usual portal submission process, but the UI offered no clues about what state I was in or how to get out of it. I think the Portal UI needs some tidying-up here. *Greg K*
