This could be a problem with the creation of player terrain that caused the game engine to simply fail. If there is a conflict between jarv ult and ornns ult, more than likely the engine stopped (server side) to prevent any further "damage" in the code.
Edit: Damage as in, the normally temporary terrain becoming a permanent artifact for that match. As in the virtual "shadow" of the two ults still being processed as an object either with the visuals permanent also, or not- leading to seemingly invisible obstruction of paths and possibly further corruption of champion/minion future way-points (for that match).
Just an example, hell I don't even know what Ornns ult is I'm just familiar with how code can... slip up. Its easy to see how something like this could get past beta, maybe not obviously for the players however since J4 is meta.