Hey there. There was a change to how emblem ownership was handled in Season 21 (mid 2023). You used to be able to, by linking your game account to another Bungie account, gain access to the emblems on that account, pull a copy onto your character, and then disconnect the linking. You'd keep a copy of the emblem on your account even though you didn't own it on your own Bungie Account and therefore not in your Collections. Some people paid for this, to be able to pull rare and exclusive emblems. Your situation is more of a reversal of this, you have an emblem an old Bungie Account on a character, and then at a later date, linked your accounts to a fresh Bungie Account that didn't own them. You still had the emblem on a character and it was still usable, as per your screenshots. Season 21's change made these emblems become unavailable. Because you've linked your account to a new Bungie Account, that emblem 'belongs' to previous Bungie Account, not the one you are currently using, that is why it says the emblem is not owned, and that's why it can't be used.