Zoom Breakout Room Options/Allocations Not working

Hi I use Zoom Breakout rooms regularly for training. Today I had a group of 60 participants. When I went to allocate them into break out rooms the option to for zoom to allocate automatically was not showing in the options. 

I had add rooms and then manually select and transfer 60 participant across to the newly created  individual rooms. 

I have gone in and rechecked my Account Settings and this already had  the Breakout Room feature turned on. (so breakout room automatic allocations should have been possible).

What can I do to fix this and why is it occurring? 

Anna