Hey, have the same problem me and my friends, just wrote a message to their support and waiting for their answer.
Ok to make it clear, if you start posting on groups using the access token you got the error message 400, but if you start posting without loading the access token, your post will be successfully posted, but without clickable image.
This is not about content, try posting any url and you will get the same problem with all you facebook accounts.
Created new facebook account today and joined one group to test, the same problem.
I think this is a problem with the API, facebook blocked ninja blaster.
Not only ninja blaster but all alternative software like ninja blaster; just triend mass planner and the same thing, no images when posting.
Waiting for them to find a solution for this.