both of these can occur when an estimate is changed and continuous adjustment takes effect on the file

continuous adjustment basically reduces the ftb or ccb drastically to try and stop an overpayment at the end of the year. ftb reduction is mandatory, ccb is up to the customer. it should be discussed as it happens if the customer is involved in the processs

sometimes though, customers will have this happen without their express knowledge (this is rare) - essentially if they have an estimate in place that is less than what their actual income is from the previous year (so last year dad earned 100k, this year his estimate is 50k), the information received from the ATO triggers a warning letter to the customer to contact and revisit their estimate to ensure it is reasonable. if they don't get in touch with FAO within the set time frame, their estimate will be automatically lifted from what it is currently, to last years income PLUS 5% (ish). at that time, the mandatory adjustment of FTB occurs (which may restrict the customer to a zero payment) and whatever option they currently have in place for CCB (it defaults to continuous adjustment) also comes into play.

another "possible" for the centrepay customer would be if they have a debt for FTB (or another payment) that they have to start repaying - the debt will always come out before any centrepay deductions (after reductions based on earnings etc - debts are number 1 priority)