3814660 - Why was my trip cancelled by the Automatic Trip Cancel Service?

A user has booked travel, but the trip was not ticketed and they received an email advising that the system has identified it as an Unfinished reservation. The user believes they had completed the trip.
Why would the reservation not be ticketed or be marked as "Unfinished"?
How can users avoid this scenario? And when it does happen, what actions are taken by the system?

A user has booked travel but instead of being ticketed, they receive an email advising that the system has identified an Unfinished reservation, though the user believes they finished their booking. A Unfinished reservation can happen if the user abandoned a booking or did not finish it correctly. , KBA , CON-MOB-TRV-HTL , Hotel , CON-SRV-TRV-RAL , Rail , CON-SRV-TRV-ADM-LAN , View Airlines , CON-CA-TLS-IEM-IMP , Import Credit Cards , Problem