I added some diag_logs to InventoryOpened EH to compare the netID of the containers.
As you can see client repeatedly opening and closing inventory will cause the "Error: Object(4 : 3) not found" message on the server.
// Server 16:26:01 Error: Object(4 : 3) not found 16:26:04 Error: Object(4 : 8) not found 16:26:04 Error: Object(4 : 9) not found // Client 16:26:01 "DEBUGGY: _container NetID: 4:3" 16:26:01 "DEBUGGY: _secondaryContainer NetID: " 16:26:02 "DEBUGGY: _container NetID: 4:4" 16:26:02 "DEBUGGY: _secondaryContainer NetID: " 16:26:03 "DEBUGGY: _container NetID: 4:5" 16:26:03 "DEBUGGY: _secondaryContainer NetID: " 16:26:03 "DEBUGGY: _container NetID: 4:6" 16:26:03 "DEBUGGY: _secondaryContainer NetID: " 16:26:03 "DEBUGGY: _container NetID: 4:7" 16:26:03 "DEBUGGY: _secondaryContainer NetID: " 16:26:04 "DEBUGGY: _container NetID: 4:8" 16:26:04 "DEBUGGY: _secondaryContainer NetID: " 16:26:04 "DEBUGGY: _container NetID: 4:9" 16:26:04 "DEBUGGY: _secondaryContainer NetID: " 16:26:04 "DEBUGGY: _container NetID: 4:10" 16:26:04 "DEBUGGY: _secondaryContainer NetID: " 16:26:05 "DEBUGGY: _container NetID: 4:11" 16:26:05 "DEBUGGY: _secondaryContainer NetID: "