The problem was that my capacity was 200. I trained about 150 in one group. Then trained 94 in another. The second one was set to pending. I then built two more barracks to bump up my capacity to 300 and i had the ability to have 4 training groups. Even though I built additional barracks my second group would not train until after the first group even though there was now space to start training.
You might want to code it so that a pending group will start training if additional barracks are built to allow it. As it is right now it seems once set to pending it will not train until the previous group is finished even if you build extra space.
Capacity at the start of training is important, not after start. That increase will be important when you start training next time. And i think it wont be changed.