Instead, you must select from a set of pre-defined options. One of these options is for nylon... and requires a heatup to 285C. Which the printer obviously can no longer do.
Now, after I badgered (and got severely gaslit by) the devs dealing with the firmware, the limit was raised from 275 to 280. This resolves (at least once released!) the issues with the first two examples, but not the third! (cont)