@rfc2822 thanks for the troubleshooting.
I will report to cPanel, possibly via my hosting service provider, and keep everyone posted on the progress.
The following is the update from the hosting service provider.
According to cPanel reply, the issues was relate to Horde:
Once Horde have resolve the issues, cPanel will including the fix in next cPanel update.
You may consider to add the event at webmail for now.