How the setting "Incomplete registrations count against Capacity/Inventory for __ minutes after their last modification" works
When a registrant starts the form process, the system actively monitors the registrant in the system's memory. This process tracks and reserves the inventory that the registrant selects while the registrant is incomplete. This process prevents overbooking. If the registrant stops going through the form and the configured time limit is reached, the system cancels the items that the registrant selected (agenda items/sessions). The system returns the canceled items to the inventory pool.
As the registrant uses system memory, the system limits the number of spots available for each form. This limit can range from 150 - 900 slots based on the current system resources. Once the limit is reached, the registrant sees a notice on the form that the form is unavailable. If the registrant waits, the form checks every 10 seconds to see if a spot has freed up.
When the Plan > Options > "Incomplete registrations count..." setting has a value of 5,000 minutes, an incomplete registration that does not continue through the form to the Confirmation page takes up one of these system memory spots for 83 hours. The system default of 10 minutes is usually enough. If more time is needed, increasing the setting to 30 or 60 minutes is often sufficient.
When adjusting the time, the event configuration must weigh how long a registrant might pause in the form. The event configuration must also weigh how long the inventory should remain unavailable to other registrants. The event configuration must also weigh how many people the event expects to register within that same timeframe. A higher configured time allows an incomplete registration to pause on the form longer. A higher configured time also limits the number of registrations that can access the form simultaneously. A higher configured time and a higher expected number of people make it more likely that registrants experience instances where the form is currently unavailable and registrants need to wait to register.
> NOTE - Proper management of the above settings for the event should help avoid this ever becoming an issue.