This information applies both to the UWP/WinX client as well as the unreleased Xamarin.UWP client:
In the UWP/WinX client until version 3.7.x17, the Device ID is created using the [https://docs.microsoft.com/en-us/uwp/api/windows.system.profile.hardwareidentification.getpackagespecifictoken ASHWID identifier] encoded to a Base64 string. This ID is relatively consistent but can change when e.g. a docking station with a network card is attached.
{{Version/WinXSince|3.87.18}}Starting with UWP 3.87.18, the [https://docs.microsoft.com/en-us/uwp/api/windows.system.profile.systemidentification.getsystemidforpublisher SystemIdentification.GetSystemIdForPublisher()] method is used to return a unique system identifier based on the app publisher ID.
The ID is generated either using a Trusted Platform Module (TPM) if present or a Unified Extensible Firmware Interface (UEFI) if present.
If neither of these sources is available, this method will return an ID that is backed by the Windows registry.