Here's a very short video of Lyra making a mistake on her "stay".
I don't ignore the fact that she breaks, but I go to great lengths to keep her engaged, even though she's made a mistake. This is particularly important in this training session because Lyra's working for personal play only - no toys or food are available, and she knows that.
Just help the dog; it's no big deal. Really. She won't take over the world. She won't think she's "getting away" with ignoring me. She WILL stayed engaged in the game, and that's the hardest thing to get back if you manage to lose it.
I put her back with a cheerful attitude. I then reward a stay. Finally, I repeat the originally intended exercise (a recall).
If she had continued to fail, I would have accepted that I was asking too much. If that is the case, ask less and start over.