Have you already done flex on models before or is this your first? It's been a long time since I did flex, so I'm hesitant to just "jump in" with advice except to say that I remember there are a few modifiers which are a little quirky to use. For example, doing things out of the "expected" order or clicking back on the modifier after applying it can put things into unexpected states. Wild guesses from a rusty radio, though.
