LUT export does not match original grade

I am trying to export my color grade as a .cube file and am having trouble getting consistent color.  The photo shows the original grade on the left and the .cube imported immediately back in to the project on the right.  The difference is obviously subtle in most of the image but pretty noticeable in the highlights.  I had no effects or masks or anything other than basic lumetri settings on the original grade.  I am using a rec709 conversion but it’s applied the same for both and should be the same output.  What am I missing?  I’ve tried playing with all the color space settings but this isn’t an exporting issue so it seems like color space shouldn’t be a problem as this is a pre-export issue.  Any ideas?