One of the possible reasons for that is the setting in the Channels --> Terminate Subs --> Answer --> "Path Confirm Attempts". In Abacus, the terminating side will up-count the call completion counter when a call is set up AND the appropriate path confirmation signal is received. If the system is not detecting the path confirmation signal immediately after sending it, it would not up count the call completion counter. At this time, if the "Path Confirm Attempts" counter is not 1 (default = 2), the system will not report an error. Instead, it would initiate a second attempt. In case the second attempt is running well, then there will not be any error report output to the GUI. Note that the call completion will not increment upon the success of the second (or subsequent) attempts.