After more fiddling, I figured out that when certain commands are included in the custom start g-code that the built-in start codes were converted into a comment. Then, even when I removed my custom code, it didn't return to inserting the default codes. Only after I deleted the generated comment from the top did it generate temperature codes. The comment seemed to have unicode errors (?) since there was gibberish at each of the ';' characters.
Working now.