I haven't tampered with anything.
Unfortunately I didn't notice what action caused the VI to go from working to broken since I made several changes to my program before testing it. My guess is that it was caused by having a build text with many parameters that have been shuffled around, deleted or added (sorry, that's pretty vague).
I will pay closer attention in the future, since I have had some mysteriously broken build text VIs in the past too (I just found out today you can convert to normal VI and inspect the code so I can't prove this issue has ever happened to me before).