For some odd reason, Minecraft seems to be linking to my Microsoft account, then forgetting it each time I open the application.
Various UI components in the game also seem to be failing to read my account information, such as my gamer tag and my profile picture, while others read the info just fine.
I've recorded a video of this to demonstrate (apologies about the bad resolution, you can thank Youtube for that):
0:07 - The game loads in, and you'll notice how my username is showing up as "Steve", and that my avatar is failing to load. Take note how my avatar shows for ~0.5 seconds before disappearing and being replaced with the loading indicator. (I think it's reading a local version of my avatar, then failing to read my account info so it defaults to the loading indicator)
0:14 - You can see that I'm not signed in, it's warning me that my maps and the likes are only stored locally.
0:18 - I click "Sign in". Take note of how I have to click the following prompt's button twice to get it to do anything.
0:28 - You can see now that I have successfully signed in and that my account info is being read from properly (my profile pic and username).
0:34 - Notice how my avatar username still shows as "Steve" and is still stuck loading, and the button on the left says "Sign in" (even though I literally just signed in and my info is being read from...?)
0:58 - As you can see here in the in-game menu, my account's username is being read properly but the profile picture is not. Also notice how my avatar loaded in properly.
1:16 - Now the left sign in button has been replaced with the feedback button, indicating that I have been signed in. My username is still not being read properly, and the avatar is stuck loading.
1:20 - I restart Minecraft to demonstrate the fact that it is not remembering my sign-in.
1:27 - The game loads in and....we're back where we started. I'm signed out, and nothing is being read from in regards to my microsoft account.
1:52 - Here, I open the "xbox console companion" app to show that I am indeed signed in to my microsoft account.
Not entirely sure what's going on here, but this definitely seems like it's a mix of a UI bug and some other bug.