Zojja's Claymore dissapeared
Transmutation combines two items, and only ever two items. When you transmuted your Zojja’s Claymore with your Vision of the Mists, your two items were Zojja’s Claymore and Vision of the mists. It remembers the stats and look of both. Later, when you transmuted that greatsword with a white greatsword, your two items were the Vision of the Mists (Because you selected the looks of that) and the white greatsword (because you selected the stats of that). The “correct” method would have required you to use a splitter to separate the original transmuted greatsword, then transmute both to white greatswords, then split the ascended greatsword on the new character and apply the skin to that. Rather expensive and as you said, pointless, with Account Bound Wardrobe for skins and more importantly, account bound Ascended/Legendary gear, which would have avoided the problem altogether.
Not sure if you can get your greatsword back, but definitely submit a ticket to support https://help.guildwars2.com/home (only one, or you may not get a timely response).
Genesis Theory [GT] (HoD)
Thank you for your answer, I’m gonna submit that ticket and see if they can give me my greatsword somehow. Too bad that I didn’t know that transmutation worked like that. :/