Lightsail instance suddenly unresponsive

I have a Lightsail instance for my website and it is frequently becoming unresponsive. This can be once every 10 minutes. My instance use less than 10% of my disk capacity and sustainable zone is 20% without any traffic. The status check failures is 0 (passed). The only thing is the domain for the Lightsail instance is not in Route 53, it's from third party.