The detailed answer I have had is:
When you set up a payment, and then make the payment, the system keeps a record for next time. However if you don't make a payment for a considerable time ( they say it could be as short as a year ) the system deletes the record. (seems reasonable).
I find it convenient to instruct the system to pay several bills at the one sitting. As they have different due dates I tell the system to pay on future dates. This is a normal part of the system
I am told that the system does not recognise instructions to pay in the future as "use". So if you make only future payments the system thinks you are not using it and deletes the payees record. The odd thing is that I have been using the system for several years and have had nothing deleted before.