If you are wondering why the Ice Mantle exotic is disabled, don't worry. It's as intended and for a good reason. In short, Bungie disabled the exotic due to issues regarding exploits.
If you want the exact reasoning for the disabling of the Ice Mantle, it can be seen via the tweet shown below.
In the tweet shown above, the official account for Bungie Help stated that the Ice Mantle was disabled due to issues surrounding cooldowns.
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At the same time, Hunter's Tricksleeves was also disabled due to issues regarding exploits. But instead of an issue stemming from cooldowns, the Tricksleeves were disabled due to issues regarding free ammo.
In short, players were able to get free ammo for the Forerunner weapon by using the Tricksleeves. Because of this, the exotic Tricksleeves had to be disabled and currently can not be used in the game's activities.
The Sidearm Reserves chest armor mod also suffered a similar fate, as it was also being used to get free ammo for the Forerunner.
That said, it's currently unknown when any of these exotics will be reenabled by Bungie. Hopefully, it does not take long, as exotics such as the Ice Mantle and Trickersleeves are hugely popular amongst players.
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Andrew Vaughan is a Contributing Writer at Pro Game Guides that has written guides on popular RPGs and FPS survival titles for several years. Andrew Vaughan specializes in survival and roleplaying games and has been a lifelong gamer.