I just had the same.

A few min after the refresh of available stakes i selected a 10 gem stake.
After 22min (i start a timer when i select the stakes and it was 8 min left on it) i went to arena to check to make sure noone was stealing my gems, and to my horror my 10 gems had changed into credits!

31 min left untill the stake refresh and 8 min left before i could collect.