For a few days thumbnails have not been generating for videos in rtMedia. I just checked on rtcamp’s demo also and it does the same thing.
Sorry for inconvenience.
Our encoding queue got stuck and needed manual push. Please check your old uploaded videos. You will see thumbnails for them now.
I also verified this by uploading a video on demo site - http://demo.rtcamp.com/rtmedia/members/admin/activity/6017/