Whenever I attempt to sign in on the Halo app, the sign-in window pops up for a split second before disappearing. I have seen other people with this problem ,but the fixes they were given did not fix my issue.
Yeah, this seems to be a universal Windows Store which is only just now getting the attention it needs after the release of Halo Wars 2. This exact issue is happening in Halo Wars 2 itself as well. Ske7ch, 343, and some community members are investigating the issue here. I imagine whatever work around that works with Halo Wars 2 will work with the Halo App too but I won't make that a promise.