Similar to the one, where you have to train 2 troops, the task where you have to train 3 settlers have same issue.. It won't complete. Seems like any troop training task is bugged.. Fix plz
You need to send a message in game to either the Multihunter or Support. This is an in-game issue and we can not help you on the forums with this issue.
To write a message to the Multihunter, start a new IGM and and type in Multihunter in the Recipient box.