After the 220.127.116.11 update on October 11th, the feature where you e-mail a Knowledge Article from the case activity panel has stopped working. The search feature works fine, but when you hit the "Link article to Case and e-mail content" button, an error is thrown, where you can download file you see en the forum post below. Sending from the new Interactive Service Hub still works.
I suggest Microsoft to make it working again.
Note: I also submitted on forum: https://community.dynamics.com/crm/f/117/t/254538