Uvmap distoretd after Boolean Union

I’ve used the Boolean modifier countless times and have never had this problem until today. When I combine the two meshes my uvmap for one of the meshes turns to dots. Not vertices but dots. I’m not sure how to explain it. If I click on a dot in the Uvmap window a face is selected in the 3d window.
Here’s a pic of the uvmap. The uvmap on the left is the affected one.



Does anyone know what is causing this? Is there anyway to salvage the uvmap?
Thank you so much on advance!

So where is the .blend file we are to look at ?