This is actually a huge problem, and has been for years. If you take any unpaid leave that brings your hours to below 19 in any one week, if the Department become aware of this, they will ask for the money back for that week. If your average over the year drops to below 19 per week, they may ask for all the money back for the year and refuse your new claim. There are arguments to say that this is not in accordance with the legislation, and also they often make mistakes in the calculations. The Appeals Office are much more sympathetic and flexible in their approach. If you have a decision made against you, you should appeal.
It is further complicated by the COVID situation, where lack of access to childcare due to COVID is considered by the Department to be equal to lay-off and therefore does not affect WFP entitlement.