There is a thread on the US community discussion boards indicating a possible conflict between the new listing tool and some common browser add-ons including Ad Block and Duckduckgo. If you are having problems with item descriptions appearing blank when listing, try temporarily disabling Ad Block and Duckduckgo, or use a different browser that does not have those add-ons installed when listing.

See the US thread here:

https://community.ebay.com/t5/Selling/New-Listing-Format-description-does-not-show-up-in-the-listing...