How to format size variants in the product CSV file?

Hi,
I have a formatting problem with sizes variants. I import the products with a CSV file.
I can select the sizes 36 ⅔, 37 ⅓ and 38.
But for size 38 ⅔ I can’t click on it and select it. If I change the number 38 in the editor, it works again.
How do I have to format here so that I can also select “⅔” as the size?
pls can anyone help me?