According to reports on Reddit, it seems that some users are having trouble with the feature. Apparently it seems to cause the microphone in their Android devices to stop functioning, and also it seems to be interfering with “OK Google” for Google Now, which is why Microsoft decided to pull the feature.
Microsoft has yet to confirm the reason as to why, but for now that seems to be the popular theory. That being said it’s odd that the feature was only disabled for the US market since if it was a broken feature, it should be disabled for all markets, right? Some users are also wondering if it might affect the integration with Cyanogen OS.
Perhaps the reason they pulled it could also be due to licensing/patent issues, but either way if you do want to keep using Hey Cortana on your Android device, we suggest skipping the update, but if you’d rather not use a buggy feature, head on over to Google Play to get your hands on the latest version of the app.