...then you have two simulations...? How is this a "logical inconsistency?"
Your post is confusing to me—I couldn't detect any actual objections or issues with the simulation hypothesis in it.
And, of course, they might diverge for various reasons (inherent randomness or intentional tweaks in one of the simulations) at arbitrary time, reinforcing the idea that there's not one entity in two simulations but two separate entities, even if they happen to be identical at the moment, no matter if you run simulations in parallel or sequentially.
In such cases, the question of "which is the true one" is really empty, there's no meaningful notion of trueness, all instances of a similar entity are equally valid. If we'd be making copies of sentient entities, then perhaps we might want to define some distinction to privilege one of the copies over the other (e.g. in mind uploading the physical/original entity over the upload), but if the simulations are equivalent then that distinction between copies/instances is just arbitrary and all of them essentially are just as valid.
> Entities in each simulation are separate instances, no matter if you run simulations in parallel or sequentially
Things can't "happen" to be identical, they are (one). E.g. I write the concept of the number 3 in a hundred different languages, fonts and styles. They are all the same, only their hosting representations are many.
I think our disagreement boils down to whether you accept or reject this.
> "which is the true one" is really empty, there's no meaningful notion of trueness
> simulations are equivalent, then that distinction is just arbitrary
Exactly, so you agree?
Furthermore, the changes depend on a large number of factors - potentially the whole simulation - so unless we're certain that the simulations are fully deterministic and without any interference (and we can intentionally ensure that they're not), there's no reason why they would stay the same. We should interpret every simulation as potentially bifurcating an exponential number of times, and each simulation explores just a tiny subset of the theoretically possible futures of each entity; and if you have "snapshots" of simulations, then you can explore many possible intervention-based branches from each point, just as we do in our experiments with simulated worlds.
The appropriate analogy is not the concept of the number 3, but a reality of a number like "0.3" that may get represented as 0.30000000000000004 in one simulation due to floating point approximation, and get corrupted by a cosmic ray bit flop in another one - and we're talking about the properties and experiences of these nonperfect instances of simulations (since if assuming the simulation hypothesis, that's the experiences we get and care about), not about the properties of some theoretical concepts that may be the "core of the entity" (e.g. Plato's philosophy) since they're not real unless/until they get actually implemented or simulated, and if the realization does not match the ideal, if there are any differences whatsoever, then the realization is the one that matters.
The steps it can take from that point may still exist Platonically.