I am also new to the A10 and just completed the training.  I found the space bar to be finicky, but not broken.  Sometimes after pressing it, it would take another minute or two before the lesson continued.  Just press it and wait until you reach the next mission sequencing point.  I never had it take more than 1 to 2 minutes, so if that’s the case then perhaps it is broken or you are flying in the wrong direction.  If you circle back around to the previous waypoint, it may trigger the next sequence.