The middle perk tree for arm pieces is glitched. I have two legendary arms that I started upgrading yesterday, but the top middle perk (fastball) appears as not upgraded and won't let me unlock it. Whenever I finish a crucible game or sparrow race it says that the perk is unlocked, but then when I inspect it there is no green bar around it and I can't equip it. This is happening on both of the legendary arms that I have. Here's a link for proof: https://www.bungie.net/en/Legend/Gear/1/4611686018430162568/2305843009217548058 You'll have to inspect the arms to see the glitched perk.