Tobius, it's best to prepare yourself knowing a lore item you already own may drop again.
Either transfer the item to one of your alt. Or camp an alt close.
There is also the option to drop your item on the ground, loot the other one, run some (for around 1 or 2 mins) and drop it, then go back to take your old item. That's if the zone is empty or you know you dropped it in a safe place. The idea is that each time you drop the item again on the ground, it refreshes the 5 mins timer.
You can also stick to one safe place doing the previous technique until somebody else comes to pick the 2nd item.
Also, as some people pointed out, sometimes there is a bug where an item disappear. It's actually on your cursor but you don't see it (you may receive a msg saying you can't loot other items due to that). Camping and coming back usually solves it.
Sad thing what happened to you. But it's all about preparation
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Daimadoshi, Arch Magician <Divinity>
Kurth, Warlock <Divinity>
Kaska, Phantasmist <Divinity>
Fuam, Druid 57 <Divinity>
Willo, Cleric 54 <Divinity>