Unless I'm mistaken if you can see all the traffic a sender can be identified by being the first node to produce a set cyphertext. As the delays seem to be fairly short for the acknowledge messages, there is some chance that the receiver can be identified in a similar way.

eg node A broadcasts C1 which has not been observed before nodes B,C,D propagate the cyphertext C1 node D broadcasts C2 shortly after receiving C1 nodes A,B,C propagate C2 etc

Of course seeing this pattern in practice might be hard, but it still seems like a possible attack vector given the current system.

Not at the exact same time they don't. You watch the propagation of the message.

What does that tell you?