Not able to join some challenges

[Janus]

http://gyazo.com/9e6b4ee9307519c9d1224d15d61baf3f
http://gyazo.com/b557d9ad9df626a26a96d110770489ee

~ 6:08am UTC (at the time of this post)

EDIT: I was just now able to join the same challenge (I think it's the same one). I didn't reload the game, but I did complete tribal smash gold challenge inbetween the above screenshots and this one:
http://gyazo.com/076705191c8f3e5ec7562369b425bdc8