My coworker, Gary Man, found the root cause as following after some deep diving:
One parameter (GET_VENTS) in .alarmrc files (e.g. .alarmrc-ABC, .alarmrc-EDF ) of Spectrum server was set to false. The default value is true. So change it to true and restart Spectrum Server will fix the issue:
GET_EVENTS=true
Thanks Gary!!!
Also Thanks for Joe's response and efforts!
William