In my experience GPT-4 does much better at handling sentences without punctuation than most people do. I think this is because as a human we might start to interpret something a certain way before we get to the end of the (possibly punctuationless) sentence and then we get stuck a bit where it's hard to adjust... but GPT-4 is trying to generate something based on probability, and all of the wrong interpretations that we might get stuck on are less probable than the proper interpretation (on average). Of course this is just my pourquoi story and I haven't done any actual tests.