Signature Check Failed

I know this is a newbie question, but...

I have not updated my watchApp for around three months till I tried today and get "Signature check failed. All app versions have to be signed with the same key pair."

The App ID is the same on the new file as the existing file.

I can see the id on the existing app in the App Store: Manifest AppID: 5351ff702e074b5f82bb2fcafd377add

and on the update it's:

<iq:application entry="main" id="5351ff702e074b5f82bb2fcafd377add".  character for character the same.

I did upload a Beta version of the app with a slightly modified id for testing App Settings, but a) I have deleted the Beta version and  b) I have restored the original id to the production version.
It feels like a caching issue so I rebooted my desktop and re-generated the export .ip file.
Any ideas? 
Mac Monterey 12.5.1
VSCode 1.17.1
SDK 4.1.4