The 16:9 crop and preview has stopped working?

I have checking file / edit / setting and the 16:9 is checked.

What the heck did I click to turn this off? I would like it back again so I can see where the crop is in Lightroom while editing my files.

THX

You have to initialize the sequence after setting that preference, to see a change.
But you could as well just set the crop directly on the keyframes in Lightroom, make sure to select an aspect ratio of 16:9 there then and copy/paste the crop as you edit from one keyframe to the other!