If you haven't yet, try completely uninstalling the application, manually deleting the app's intermediate and output directories (bin and obj by default), rebuilding, and re-deploying. Also, inspect the project file itself to ensure there are no lingering references to 100.0. There is a known limitation (see the Known Limitations section in this doc) that requires some manual editing of the project file when upgrading from 100.0 to 100.1, but that generally causes a build failure. Still, it's worth checking that no old references are unexpectedly hanging around.
I would also suggest, while troubleshooting, have your app only create the basemap using Basemap.CreateStreets() instead of Basemap.CreateStreetsVector(). There is another known limitation that vector tiled layers do not render on the Visual Studio Android emulator. Although you're not using the emulator, sticking with the image tile basemap will rule out the possibility that you're running into a similar limitation on the particular devices you're testing with.
