Once you use/give the item, even if it's old, as game only saves for every 3 or 4 minutes, in that time if server crashes then it would be lost.
To avoid these problems, relogging is the only option.
Again, sorry for the inconvenience.
Items lost in rollback cannot be returned. Sorry for the inconvenience.
And yes, once you logout, it forces the game to force a save, so you won't loose anything after you have logged out.
Thank you for the answer.
I checked every single Pokemon in every single box of the PC, but it's not there.
I didn't lose it due to rollback because I've been using it for at least a month.
If you just give the item to any Pokemon and if server crashes, no matter how old the item is, it will be lost.