It came as a big 'yes' to Windows 10 Mobile when Starbucks launched its official app on Windows 10 Mobile a year ago. Unfortunately, a year on, the outlook for Windows 10 Mobile isn't positive, and more than ever we are seeing its slow demise, with apps big-and-small leaving the platform, and even Microsoft restricting the updates it delivers to the platform, mostly containing just fixes, rather than new features.
As the outlook for Microsoft's current phone platform worsens, it appears Starbucks has caught on, and is removing its app. Users are reporting (via Reddit) that the app is forcefully logging them out, and then displaying a message that recommends they use a Web App at app.starbucks.com instead (which, interestingly, contains more features than the original Windows 10 Mobile app):
There's been no official acknowledgement from either Starbucks or Microsoft, but it is worth noting that Microsoft's CEO, Satya Nadella, is on the Board of Directors at Starbucks.