Thank you for your post. Unfortunately, when you get a new device the map features and custom maps need to be transferred over. That information isn’t stored on a server or saved in a cloud. All of the information is saved locally on the device. This is to ensure greater security for the data. All of the custom maps and map features are associated with the app. If you delete the app, all of that information will be deleted too and cannot be retrieved.
The Map Store account is only used to hold your purchased maps from the Avenza Map Store, it stores maps that you have already paid for so you don’t have to purchase the map again.
The Subscription isn’t an actual account that holds anything, it only gives you access to certain features within the app. Such as unlimited map imports.
The functionality you are requesting is a feature request that we want to implement in the future. That way users can backup their map features. I’ve gone ahead and added you to the feature request so you will be notified when it is implemented.
Lastly, if you have created a backup of your old device or of the app, you can restore it from that backup. Unfortunately, I can’t give you another workaround or fix.