Interesting. Any chance you're accidentally transcribing the en sound as "n" instead of "ŋ"? This is an easy mistake to make, and perhaps one we could recognize proactively to display a more helpful error message.

To double check: if you type the word "blank" into the text entry box at the bottom of the screen, you should see it automatically transcribed (i.e., automatically "blæŋk" should appear in the grid).

FYI, the underlying JSON file derived from CMUdict is at https://github.com/jmandel/heardle/blob/main/words.json (it's, uh, 10MB, but it's hosted from a CDN that supports gzip encoding so "only" takes one megabyte to send over the wire.)