This happens when you lose connection to the game servers mid-battle. Your battle had started, but before you had deployed all troops your connection was lost. The game servers will only have registered the troops you deployed before losing connection.
Most, if not all, Stormers have experienced this at least once, and we know how frustrating it can be.
Before starting an important attack, hook up with a solid wifi network, or at least a solid 3G/4G connection with a reliable carrier. Full wifi bars or coverage alone is not always enough to guarantee a solid connection, because local networks can slow down and get overburdened at times. This is especially true if you play in a moving vehicle or on underground public transport, or someone is streaming videos in your network.