Hello Yong,
Enable logging on your ASA and next time the issue happens make sure you have the timestamp so you can correlate the events the system logs states when the issue happens!
Then U can provide us the logs
For more information about Core and Security Networking follow my website at http://laguiadelnetworking.com
Any question contact me at [email protected]
Cheers,
Julio Carvajal Segura
Julio Carvajal
Senior Network Security and Core Specialist
CCIE #42930, 2xCCNP, JNCIP-SEC