And if the attacker releases the block within the propagation delay so that some see the block announcement before they see the lock announcement. So there is an ambiguity. Which is correct the instantX announcement or block chain announcement?

Some might argue that attack seems solvable by making the delay on instantX confirmations a sufficient number of seconds (or what ever is the maximum propagation to every PoW mining node). But the problem is that P2P network for propagation can be Sybil attacked so some nodes could be isolated and controlled as to which announcement they receive first. So it is possible to use this as an amplification attack on PoW resources so as to effectively control much more PoW resources than you do control.

It isn't necessary to isolate propagation to a majority of nodes. The rule about propagation for InstantX is supposed to be cast in iron, meaning that any node what has seen a certain propagation order will forever ignore the chain that has decided the opposite ordering, thus you end up with massive forking. An attacker could force Dash into an unlimited number of forks and kill the coin. The only solution is my invention mentioned below. But in Dash's design that would require adandoning instant confirmations (for the reasons I explained upthread to monsterer ... or wait for the white paper for diagrams and eloquent explanation).

I am also concerned about Evolution and that the quorum must change periodically, so if on the next block the quorums are changing then an attacker can construct a spend on one chain with one quorum, and then on a hidden chain on another quorum, which is not illegal as the quorums have changed and the miners who are mining on that hidden chain are thus ignoring the announcements on the quorum which from their perspective no longer has permission to sign the transaction. The basic problem is that around the time of changing quorums, there is no objectivity as to which quorums are authorized. Thus two chains can spend twice. And so then the hidden chain is announced later and it is longer so it wins and the double spend has been achieved. Since Evolution promises these to be instant confirmations, the merchant will have long since assumed the transaction was irreversible and not have waited for 6 blocks or what ever is safe (assuming the attacker doesn't have 50% of hash power). Remember that hidden chains can be created with less than 50% of the hash rate. The basic problem is that propagation is misaligned with orphaning. There is only one way to solve this fundamental issue about ambiguity and that is my invention I published in 2014 to defeat selfish mining by including all the chains but you can't do that in Dash's design for the reasons I explained to monsterer.

Dash has more attack holes than Swiss cheese. And I will be explaining more of them which monsterer inspired me to realize. I use that euphemism because I want to spank speculators who think they know what they know. They don't. These technologies are much too complex for speculators to have any reliable clue about what is what. Illodin you are reasonably informed being a programmer yourself, but still you will miss some of the finer details because this stuff is not easy. It requires a lot of experience and thought to master. I even messed on these at times. It is quite complex.