I have an attribute that is a core Attribute for Magento 2 that is not sorting on the front end SORT BY:
The attribute is Quantity and Stock Status….. I import to it by using ( qty) in import field header.
It seems that it is not configured properly. I am not sure if it was changed when importing and exporting the attribute.
Magento version: 2.1.7
This is not a module's bug. The issue happens in Magento 2.1.7 when saving attribute quantity_and_stock_status.
Since the attribute gets the data from the source model, the issue happens when saving attribute without checking enough conditions.
If you have this issue, please override controller validate of core Magento to fix