I asked the Xbox support team about this, this is my chat log with them:
XBOX Support team: Hello Erick, thank you for reaching out to Xbox Support, We apologize for the inconvenience caused, But can you please elaborate more on the issue your having ?
Me: Sure. I don’t know why this happens, and I’m not the only one experiencing this issue. I’m also not sure if this happens with every single game available on the PC Gamepass, but it certainly always happens with Conan Exiles. Everytime Funcom (Conan Exile’s developers) releases an update, it becomes instantly available in stores like Steam or Epic. However, it never shows up in the PC Gamepass on time. The first time I noticed this issue, I was trying to log into an official online Conan Exiles server, but it showed up as invalid, even though my Steam friends could join in immediately. This went on for days. Even after clicking the “Search for updates” button, it never said there was an update available. I read in a forum that the only way to solve this was either waiting for up to a couple of weeks for the Gamepass to make the update available, or to reinstall the game.
What I don’t understand is, why does the game comes with the update included if I reinstall it, but if I don’t reinstall it and I only click the update option, the Gamepass says there are no updates available
This is a major issue as Conan Exiles is mainly an online game, and if I don’t have the latest update installed, I just can’t join the official servers. It’s not an appropriate solution to reinstall the game every time there’s an update just to be able to play, as the game size is 90gb.
Yesterday there was a hotfix and Steam and Epic users were able to install that minor update with no issues at all, but us PC Gamepass users either had to reinstall the game, or wait for the update to be available. I tried to update it in the morning, and the update was not available, I tried again in the afternoon and it still wasn’t available. As this has happened before, I just ended up reinstalling the game for the fourth time since I started playing. Once again, how come if you reinstall the game, it comes with the new update included, but such update always takes way, way, way too long to become available for everyone who already has the game installed? Sorry if I repeated myself too much, I wanted to be as clear as possible with what the issue is.
XBOX Support team: We apologize for the late reply, it’s due to the high volume of messages, Can you please try on a different game to see if the issue with the game itself ?
Me: That’s not how game updates work. How could I know when a game is going to be updated so that I download it before the update comes out?
XBOX Support team: We apologize for the inconvenience caused, But when we check the updates for games are pushed by the game developers.
Me: So, let me get this right
My Steam friends have been able to play Conan Exiles with the new update for almost a week now.
I uninstalled the game and installed it again, and I also have the update.
But my friends who play it through PC Gamepass who have not reinstalled the game like I did, can’t play the game yet, because the update hasn’t been released on PC Gamepass Even though Funcom told us they release the update for all platforms at the same time.
What gives? where does it go wrong?
XBOX Support team: Hello Erick! We are terribly sorry to know that you are going through this. Please accept our deep apologies for the inconvenience. We would like to inform you Erick is this is something that the game developers must address because we have no control over the game’s updates. The only thing We can advise is to avoid reinstalling the game when there is an update for it is to go to the Microsoft store on PC, go to the updates tab, and try starting the update from there rather than from the Xbox app. Can you also please verify that Xbox app and all gaming services is up-to-date including Microsoft Store and Windows OS. We will be looking forwards to your reply. 
Me: I did exactly what you told me to. I checked for OS and Microsoft store updates, there was nothing. I then checked if I could update Conan Exiles through the Microsoft Store, and no update showed up. Today there was yet another hotfix, and it just does not show up anywhere. Not after checking for updates like you told me to, and not through the usual methods. Once again, the only solution I can see is to reinstall the game, for the fifth or sixth time now.
