Audio: sounds occasionally continued playing after quitting to main menu.
Visuals: ocean waves, camera shake, chat bubbles, resource overlays leaked across co-op sessions.
Network/chunks: lag from chunk load/unload thrash when players far apart; mid-session save load didn't disconnect old clients.
Player state: clients spawned dead/respawning after rejoin; wrong spawn positions; paused state leaked.
Entity state: flora/creatures mismatched between host and client after starting a new co-op game; "under attack" bubble fired on save load with no enemies.