Ftb decreases fortnightly

[CinderToriella]

Does your FTB drop when your child turns 5?

[briggsy's girl]

Part b drops when your youngest turns 5
Ftbb isn't impacted directly by maintenance however if you have a perceived ftba overpayment due to maintenance/child support, all payments are adjusted (a,b, rent) to counter it. So changes in child support would be your most likely culprit