A little late, but fi your still interested. This happens when the game is trying to pull one of the red Injure/Ammo markers from their "bag" and place it.
The code defines these bags via their GUID but only uses 1 guid for all 5 bags (meaning if that 1 bag is missing (left player), all other bags are also nil aka non existent).

If you'd like you can open the tool in the editor and go to line 581 & 583 and replace the values with {'44d73d', '1ab810', '76b05b', 'ec22d8', 'ecb86b'}, That should fix the problem. If it doesn't check all your red square "bags" manually and insert the guid from lef to right.