I may have just stumbled upon what is causing this issue. I think it is related to the fact that the entire script gets parsed again every time you make an update. So, for example, if you are typing a message in the Display Message node, each character you type triggers the parser to run. With the growth of the parser, it would be more noticeable now too, especially the longer the script gets. At least as a temporary fix I could probably have it not run the parser until the text box loses focus.