Following log file needs to be checked-
C:\Program Files (x86)\SapphireIMSAgent\Log\SapphireIMSAgent.log
Along with current log file (latest) file you may need to check backup logs available with extensions log.1, log.2, log.3, log.4, log.5 as failure log messages might be overwritten with some other logs in current one when log file exceeds certain size.