Good news, I got my maps back. The Subaru Customer Support replied quickly with a detailed step by step procedure to regain the maps. It looked a bit daunting but with patience it worked.
The only hitch in the process is that the USB stick has to be plugged in after opening the map update window. It didn’t register when I first put it in.
I will copy the steps below for anyone else to use.
This is the email reply I received:
Thank You for contacting Subaru (UK) Ltd.
I will try and help you with your map issue, if you have lost your UK map, it sounds like you may have started a UK Map update 'in car' via a Wi-Fi connection, and then it lost connection/lost connectivity - the first thing it does is delete the current map, then apply the update, if the update fails, you have no map...
The only way to fix this now is to carry out a FULL map reload via USB stick, using the maps website.
I'm going to give you all the information, so apologies if you are much further ahead.
For your information, the maps installed on your car can be updated to the latest map release using website: http://subaru-maps.com
When using the subaru-maps website you create a user-account, add your vehicles VIN, type in your Request Code off the Head Unit to obtain your Authentication Code, then download and install the 'Map Downloader' app, open this and log in (also using the same credentials as the website) to view and physically download any updated maps available for your car.
Once the USB stick has been created, insert it in the car, then type in the Activation Code you obtained from the website when prompted to authorise the install.
I know this all sounds complicated, so I have attached some visual instructions as a PDF - I hope these help explain the process a little better.
Lastly, the app and the QR code - unfortunately the app is only compatible for the EV vehicles, eg the SOLTERRA currently, it will not work with your Outback.
I will attach the pdf mentioned above.
Hope someone finds it useful.
Activation Code on HARMAN maps-Dec-02-2024-03-43-40-7464-PM.pdf