This is a food diary/fitness tracking site, and on it, with HTTPS Everywhere forcing secure connections to MyFitnessPal, most lists of food items don't load properly, with the following or similar appearing in the browser console:
XMLHttpRequest cannot load https://www.myfitnesspal.com/food/load_recent. Response for preflight is invalid (redirect)

Additionally, if a list is working, attempting to add an item from it to the food diary will trigger the site's "under maintenance" message, with the following appearing in the browser console:
POST https://www.myfitnesspal.com/food/add_favorites 502 (Bad Gateway)