It may have been updated.

The way I play the mission through totally is to go in to the story board section then top right it says 'Play Mission'.

Be aware that it will literally do it from your desired start ion location. For example if you have the mission start in a certain sector block you will start in that sector block.

If you want to play individual sections you need to go to the maps section and select which map you want to play with.

Oh on a side note. My problem was resolved. Thanks.