Some achievements unlock when achieved, while other achievements don't. How can I fix this?

There is nothing you can do, but wait until they unlock. Sometimes though, it could just be a bug with the game, and the developer hasn't fixed it yet. Usually when the developer fixes the issue, the achievements should unlock the next time you start the game.

Hi TheGeekyBanana, achievements not unlocking is common with the Xbox One. Some users unlock them fine, while others don't. Microsoft are aware of the problem, and are working on it. Worry not, as your achievements will unlock eventually, I know as I
waited for achievements to unlock for Destiny, and they finally did a few days ago.

I can unlock only achievement from Xbox one games,when I play on Xbox one,Xbox 360 achievement not unlocking while playing. I have a prove pic but I don't know how to post it here

Some achievements can get delayed when they unlock. If you go into the Achievements app you should see your progress as 100% for your achievements.

If this is the case, simply keep using your console as you normally would and eventually the achievement will pop. You don't even need to be playing the game you obtained the achievement in at the time. I had this with a few achievements and after a couple
of days while doing something unrelated the achievement unlock just pops for the ones you obtained.

I don't think you'll see some real incentives with achievements as people can mod them.

You do unlock some gamerpics when you unlock certain achievements. For example on Gears 2, when you complete the game on co-op, you unlock an achievement and a gamerpic. The same thing happens in A World of Keflings and other gamers, I've noticed.