Ftb decreases fortnightly

For months now my ftb changes on a fortnightly basis. I don't work, no partner and child support doesn't change that often and I'm not on disbursement method. My youngest has just turned 5 so my part b has dropped but is continuing to drop below the max rate and I don't know why. Centrelink staff just tell me it'll right itself come reconciliation time but it's getting to the point I'm having to do new fortnightly budgets because some fortnights it's a big drop. What exactly affects part b payment to make it drop. I understand my child support affect the other parts but I thought ftb wasn't

I've had 3 drops since the new financial year as well. I just put it down to the new rules which came into effect at the beginning of the financial year and the carbon tax repeal.

Does your FTB drop when your child turns 5?

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