I needed an item for a quest, didn't have any of those in my shop anymore. So I removed 10 from my gallery. I finished the quest and cleared all my inventory into my shop. When pricing said item, I only found 8 of the supposed 9 in my shop. No idea, what happened to the 9th. Account search proved, that one had gone missing.

File a ticket, they should be able to check what happened

I didn't bother to file a ticket, since it was no big deal. I only mentioned it here because it obviously was a bug and probably other people would be affected as well.