This happens to me with unidentified items if I equip them on a character in gomule without realizing they're unid, then loading in, theyll be gone forever. But only sometimes. That's the only situation where I've had items disappear, but it's happened up to including present day.
Edit: I can reproduce it and I took screenies.
1. A few unid items in gomule:
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2. Put them on in gomule: (bloodletter, duskdeep, bladebuckle, bloodmoon equipped)
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3. SAVE, then start D2R, here's the character screen (the bloodmood is already missing, but other items are present here...)
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4. In game, all are gone.
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Edit 2: Interestingly while looking into this I found out that the second and first weapon slots are swapped in gomule vs in the actual game, like you can see in the previous pictures I equipped the bloodmoon and bloodletter in weapon slot 1, whereas in game they aren't showing up in weapon slot 2. My original weapons are still in weapon stlot one as you see in this picture (and they show up in weapon slot 2 in gomule)
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