This article will guide you through understanding why an "Unlimited Member" may be showing as having Lost session credits.
In this specific situation, an unlimited member will have had to be added to the waitlist for a class. If they are not booked, the session credit attached to the waitlisted booking goes back into the account for 24 hours. If the session credit isn't used, it will move to the Lost tab.
When a booking is Cancelled OK, only one day is added unless opted otherwise when reassigning the credit back due to the cancellation not being the client's fault. The option to add additional time would need to be selected. If not, the session credit would expire 24 hours later. The 24 hour mark is the defaulted expiration time.