Auto Curves Combined turns entire image Black

A curious behaviour.

On a small number of .DNG RAW images, when I select the "Auto Curves Combined" button, the entire image becomes black. The curves graph shows two points added, but no change to the tone curve, the points just sit in "empty space". There is no detail on the image preview at all, just black. If I try to export the image, again all I get is a solid black rectangle.

Turning off the Curves panel brings the image back.

This happened only on a small number of images from one particular shoot.

Is this a known bug? Is there a work around?