After upgrading from Magento 2.0 to 2.1, product attributes no longer seem to be working. Here is an example - notice that the color attribute is a swatch, and the size attribute doesn't exist at all. Both of these used to be dropdowns.
When I visit Stores -> Attributes -> Product and look at both of these attributes, they both seem to be configured correctly. "Catalog Input Type for Store Owner" is set to "Dropdown". If there are any other options I should have set a specific way, I'm not aware of them.
The two sizes that this product should have are "1.75mm" and "2.2mm". I created a test product to make sure the product data just wasn't corrupted in some way, and when I gave the test product those sizes, it wouldn't appear for that one either. However, other sizes did work. As far as I can tell, there's no difference between the working size attributes and the non-working ones except for the name.
I'm pretty new to Magento 2, and wasn't the one who performed the upgrade, so my knowledge is somewhat limited. Let me know what other information I could include to be more clear.