Within the space of three model builds, I've gone from "Yes" returning the AMAZON.YesIntent, to a custom intent featuring AMAZON.US_FIRST_NAME, and now to a different custom intent with just 8 basic utterances with a single AMAZON.Sport slot type. Having never met someone called "Yes", nor played a sport called "Yes", I'm not sure why that is happening. There is not a single utterance outside of the YesIntent containing the word "Yes". There are also no entries for "yes" listed in any slot types. Utterances like "yes please" still return the YesIntent, but a single "yes" no longer does.
I know I can code around this issue from the backend, but I'm not thrilled at the idea of playing whac-a-mole each time I rebuild the model. This isn't just a speech issue either. Typing Yes into the Test Simulator does the same thing.