I think previously trading a new weapon to Abquhbah before completion of Coming Full Circle would result into something like:
You cannot successfully complete this trade transaction while in possession of a Serpentking Zahak relief shard. You must first finish the quest "Coming Full Circle" before trading a new weapon.
This meant one would not be able to start a new weapon if the first one was discarded for example... until the 2022-01-11 version update [1], after which it has been possible to cancel the quest, which seems to have perhaps happened here...

Do you remember a confirmation dialogue regarding it with Abquhbah?

If this is what happened, it might be impossible at this time to complete that particular Carnwenhan...

For more discussion regarding this, perhaps post under Missions, Quests, and Records of Eminence [2].

To report it as a bug, follow the guide in the welcome topic (though I suspect it would end up under Working as Intended): Welcome to Forum: In-Game Bugs!

1. https://forum.square-enix.com/ffxi/t...Version-Update
2. https://forum.square-enix.com/ffxi/f...ds-of-Eminence