I am not sure if this classifies as a bug, but there should be a fix to assist players, especially new players.
My Athena is level 7 right now, her morale is around 10. I have equipped her with Cyclops/Medusa and I just added a Griffin… as she AutoPlay, the morale bar gets full and stays that way. Obviously there is not enough morale to spawn a Griffin, but it should neglect the Griffin and spawn other units. I know the system tries to balance all the units, therefore is spawns “the same amount of morale” for all units if I am not mistaken. In this case, it’s stuck there because it can’t spawn a Griffin, leaving the Hero alone…
There could be two possible, easy fixes for this.
Warn the player when he chooses the specific unit, that his morale is not enough to be able to spawn it (this also makes people understand what morale does - we still get questions what does leadership do, what is morale and so on).
Spawn different units in that case, so if that particular unit, is greater than the total morale of the hero.
Personally I would add both.