I've found that it's easy to get people to engage in the group when they first join (introduce themself, etc.). Do you think lowering the resistance for level 2 could be a good idea? E.g. When they first comment or post it gives them a celebration-type pop-up saying they leveled up and tells them the reward they get (if there is one). I feel like this could help to give them immediate positive reinforcement and encourage future engagement.