As of recently any photos I add to a shared photostream will not update for others. Only I can see them. How come others sharing this photo stream are not getting the new photos?

As of recently any photos I add to a shared photostream will not update for others and I don't see the updated photos on my other devices. Only I can see them from the device that i've posted from. How come others sharing this photostream are no longer getting the new photos? My iphone (the device i'm adding from) shows 20 pictures in this shared photostream and yet 4 other people that I share this photostream album with and my ipad only show 12 photos. For the past week I keep adding photos thinking people will see them but it just won't update the new ones. Any ideas how to fix this?