I strongly recommend following @bungiehelp on Twitter with all notis on. You'll always know what's going on with issues like this.
Allo there, The mod has been disabled due to an issue with it and the Forerunner exotic. https://twitter.com/BungieHelp/status/1468732754971955200?t=Wu_r3KH9CwNWNsGs85LDgg&s=19 [quote]Due to an issue where the Forerunner Exotic sidearm could get free ammo, we have disabled the Sidearm Reserves chest armor mod.[/quote]