Gears of War Ultimate Edition (Windows) "Mix it Up" achievement is unobtainable

But as the TrueAchievements.com page says "Rotating playlists are no longer supported. The achievement is Discontinued for anyone who did not already complete the game types in rotating playlists."

So, to make it short. Is not possible to obtain the achievement right now

Well, I submited a ticket to The Coalition if there is a way for them to fix this problem, but knowing that players had asked the same since 2018, I don't get my hopes up.

Thanks anyway for the answer

Trueachievements (a site about, you guessed it, achievements) shows that you can unlock every other online achievement, so you can obtain every other multi-player achievement except for this one

Gears of War: Ultimate Edition (Windows) Achievements (trueachievements.com)

So the servers aren't closed

Hi and thanks for reaching Microsoft Xbox gamer's community. My name is Josef.
I'm an Independent Advisor and a Microsoft Xbox user like you.

Hope you're doing great today despite this Piyi

Yes, depending on when you start the play you can get all the achievements or not.
Sadly as you said, gears of War servers are not working anymore.

This means that multi-player achievements are not obtainable anymore.
Is not only with gears of War, this happens with basically most of the 360 games. (Even I have some locked achievements for the same reason)

Game servers are closed due to economical reasons or when the player base is not big.
Once servers are closed is basically imposible to re-open then again. Is what it is

You're welcome, time will tell

That's the sad thing when we start playing years later