My thoughts exactly. Asking once is one thing. Continuing to ask and then actively going to the back of the plane to ask again would make me suspicious, too. It's strange to keep pressing this when the end result would have been the OP downgrading himself to coach -- and just to make a minor more comfortable? All sorts of red flags go up in my mind.

I also suspect the first FA said "she’d ask" as a way to nicely stop the conversation. She likely had no intention of doing anything else as the UM was already seated and under the monitor of the assigned FA. When this kept getting pressed, I think their senses rightfully became on alert that something could be amiss.