What would it even mean for a simulation to be imperfect, though, from the perspective within the simulation? You can only observe the simulated phenomena. So it would be perfectly normal, say, if things become non-deterministic at the hardest to observe small scales, or if there were minor inconsistencies between the smallest scale behaviors and the largest. You'd just call it "physics".
See that's hard because I do call it physics, and I do not call it a simulation. I am here in this world, and from where I stand it's as real as anything will ever be for me.
My point is that I don't think there's any sense in entertaining counterfactuals that, if true, will be impossible to come up with evidence for, and I think the assertion that our world is a simulation is one such counterfactual.
That is, unless the physics gets so absolutely insane that "it's just physics" fails to scratch the itch. One example would be if we discover an artifact that lets us see each particle's corresponding unique ID such that, once we have that ID, we can then type it into a console and arbitrarily set properties like its mass.
If simulated entities gain control over the parameters that govern the simulation itself... well is it really a simulation anymore?
How to detect imperfect simulation: some unexplainable missing wavelength bands, or quantisation of results where it should be continuous would hint at "cutting corners" in simulation, like steps in energy levels from very distant xray sources perhaps?
As far as we know, our "physics" does not show any possible imperfections, or we didn't thought of all imperfections which could arise in simulation.
I think you're setting the bar far too low. An inability to explain why certain frequencies produce no EM radiation would be unsettling, but maybe reality is unsettling. It would not be enough to jump to the conclusion that nothing we've ever measured is actually real.
