Why am I not getting any bonus Games in farm heroes saga?

Nan_Leider

I had one a week ago but it dissappeared when I still had 50 hours left. I haven't had any since. This is the only game I spend money on but will not continue without the bonus games. When will the bonus games return? 

Randle

As far as I know, those come and go Nan. Also, I believe I don´t always get all of them, so maybe some random selection is being made when it comes to these challenges.