This happens to me also when my friend is hosting. Seems to not be affecting the host. The pieces I place appear when I disconnect then rejoin. This happens often when building a ship. I think I've noticed that the pieces disappear when I place the last item in the stack. Once the pieces become invisible it affects all other pieces that I place and it will cause workstations such as furnaces to become invisible when I light them (torches too). If I then sail a boat a distance from the island, none of the objects I placed will be visible when I return.