Elliptical marquee tool selection disappears in Photoshop

I'm trying to cut out an oval shape to finish a headshot.  The marquee tool draws the oval fine but when releasing the mouse button, the shape does not save.  Instead, the marching ants outline jumps to an arbitrary shape near the edge of the image.  It was fine last week.  What do I do to make it work properly?  Thanks for any advice!

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