I am able to create an AEM Experience Fragment and Export to Target successfully. I can see the XF as an Offer in Target and also able to replace activity content with the EF. Works fine in the VEC but when save the activity I get the following error 

Sync Error - Your updates did not get published to Adobe's delivery network. If the problem persists, please contact Adobe Client Care.

I've removed the Experience fragment and the Activity works fine, but the same error appears when replacing content with an AEM EF. It would be great to understand why Target will not publish. I cannot find any Fixes in the documentation or across the community.