Dynamic backup camera lines disappeared

It used to be that when I shifted into reverse on my 2015 Prius V, the back-up cam would turn on and there would be a grid of fixed blue lines (and one red line) superimposed on the picture, plus a grid of yellow lines that would move side-to-side when I turned the wheel to show the direction the car was headed.

This morning, I shifted into reverse and the blue lines were still there, but the yellow lines were gone! What happened, and how do I fix it?

* There are no on-screen configuration buttons on this version of the back-up screen.
* I have tried turning the wheel all the way left and all the way right to recalibrate.
* I have checked all the configuration menus that I could find.
* I even tried to follow instructions to turn the car on and off 5 times to enter some sort of configuration mode, but the instructions weren't detailed and I don't think I activated it properly.

Has anybody had, and fixed, this problem?