Variant Not Saving

I have a few products where I'm trying to add Small and Black but it just won't add it.

What could be causing this please?

Thanks!

As you can see from the attached I was able to add small for other colors. And the options for black and small are selected but when I save it doesn't add to the variants.

Oh and it's seems to be affecting only this one item.

I have another question.

The variant is displaying a size that is not available in the list.

As you can see from the attached, only the brown has an XL large size. On the front end when I choose one of the other colours the XL size is showing but I didn't add XL for those 2 sizes. When I click on it, is says Sold Out, but I would prefer not to have a size listed that I did not add.

Is there a way to have only the variant that is added displayed for that item.