In my view, the main problem is that nodes will see transactions in a different order so when one node submits a transaction which references two older transactions (according to this node view), some nodes will receive this transaction before receiving the “old” transactions it references so won’t be able to process it. Assuming this happens under heavy transaction load, it is not difficult to see how the whole thing gets out of control with ever increasing number of transaction which are left not referenced in the DAG or cannot be added to the DAG because of missing dependencies.