Hi Team,
When you try to add size variation within the attribute tab and when you try to add an existing attribute as size and specify a size (Ex: 8 and 9), the number 8 is not appearing in the dropdown. Moreover, the attribute is available in products > attributes > sizes.
Also, please note that this issue persists only with single-digit attribute values. When you add double-digit values, everything works fine.
Finally, whenever input values change, the input field width increases. (Ex: General, inventory, and product data panel sections)