When you get a missing in REX line on a report it shows you all the information it can but your heart can sink when it is a variable product. We know these are harder but as they slowly disappear from use (no one does multiple variations any more, colour or size nothing else!) we still need to fix it.
What went wrong - Normally it got disabled or was an error. You will see it ALSO pop up in out Incorrect Variables
The report gives you both the variant ID & the Product ID, we are going to need both.
All we need to do is go to this product and locate that ID and Delete the variation!
The product ID appears in the bar across the top of the page in your browser ...
wp-admin/post.php?post=29157&action=edit
Now we just need to find the variation to delete
Scroll down and choose variations ...
And then choose remove
OK to remove the variation
And then Update.
All done! This will not be noticed immediately but it will clean up the system for next time.