Hello Community -
As Jacob noted we are aware of this issue and are working towards a solution for the larger issue. Please note that while this issue is ongoing, you can still post your listings by manually including the CIS information you need. Once you open the Custom Item Specifics window on the lister page, you can use the "Detail Name" field to add your specific, such as "Size" and the "Value" field can be used for the value you would typically use, such as "Medium" or whatever the appropriate value is.
I will update this thread as soon as we have more information available regarding this trouble. Apologies for the inconvenience.