This can probably be tied to other issues that have already been reported, but the circumstances in this case were unique (to me) so I'm filing a report.
I spawned in to the shed of a log lodge after rejoining a server following a server crash in exp (I know, perish the thought), and I briefly saw a PU scope on a shelf as my surroundings were drawing in, but then it just disappeared as everything finished rendering in. I searched the entire lodge using the vicinity in my inventory and couldn't find it.
A moment later, my friend spawned in and immediately said "hey don't you want this PU scope for your Mosin?". For him, the scope was right there, sitting on the shelf. He picked it up and put it down and it appeared on my client and I could pick it up and attach it.
Again, probably related to client/server synchronization issues that have already been reported, but I had never experienced it before in this context, especially considering that for a brief moment I was able to see the item.