Floating Mobs and Blocks after Player's Internet Troubles

A player starts spawning mobs+building on ground, then gets internet lag and disconnects. All mobs+blocks he places/spawns appears about 20 blocks in the air. Screenshots attached show the floating mobs+blocks. UPDATE: He then re-joins only to be kicked and brought back in immediately. Problem continues, he keeps on joining/leaving without doing anything. He has to force crash Minecraft.