There are two problems and I think they are related:

• The achievements I see on Windows 10 and Android are different. I assume the xbox achievements for my account should be the same.

• When you have Minecraft Window 10 running (but aren't in a game) and at the same time you get an achievement on Android: the achievement notification will be shown on Windows and not on Android.

So I basically have 2 sets of achievements and an achievement I got on Android was added to my achievements on Windows 10.

This defeats the entire achievement system so I hope you can have a look at the problem.