In route 108 exists a spawn of 5 Star Pieces. In my account and my friend's account this spawn doesn't appear, while on another friend's account it does.

 

Please tell me what the problem is and what I can do to solve it.

You might've picked up the item in the past and not remembered it now. I did a guide on the monetary items thingy and as far as I know, that one does not respawn (isn't it big pearls though?)

 

Wait for a Staff member to resolve it, I guess.