It's starting with the assumption that the simulation would reproduce the universe perfectly; this eliminates a lot of possibilities.

Many would expect that the parent universe would be more sophisticated, potentially with more dimensions, that we can only glimpse through artifacts of the simulation.

I've always wondered how you'd be able to rigorously distinguish breaking out of the simulation from just discovering novel things about your current universe.

Is a black hole a bug or a feature? If you find a way to instantly observe or manipulate things at Alpha Centauri by patterning memory in a computer on Earth a special way, is that an exploit or is it just a new law of nature?

Science is a descriptive endeavor.

I guess that some extreme cases would be obvious - if a god-admin shows up and says "cut that out or we'll shut your universe down", that's a better indication of simulation than the examples I gave. But even so, it could be a power bluff, someone pretending to be a god. Or it could be comparable to aliens visiting Earth rather than gods revealing themselves - i.e. some entity of a larger system visiting another entity of the same system, not someone outside it poking inside.

Also that Universe could use entities similar to hard and soft links (quantum entanglement), memory deduplication and so on.

How many people did we met in the world with similar face appearances and even personalities, almost like you are finding copycats everywhere? Also, it happens as if some kind of face/shape would just have a single personality with minimal differences spread over thousands of lookalikes...