Elastic beanstalk load balancer latency stay high 80s forever after a CPU spike event

I have a AWS elastic beanstalk load balancer t2.medium environment set up recently. I noticed that there is a CPU spike event (last a few seconds), following with high latency stay at 80s forever and hanging - never auto recover until manual reboot. (see chart)

The new environment is a clone of our old instance (Tomcat 8.5 with Java 8 running on 64bit Amazon Linux/3.4.18). The CPU spike might be caused by a batch job, but why latency stay high 80s after CPU usage recover? This happened twice in 2 weeks. I checked the log, no other suspicious event.

The old instance (t2.small running the same code) had never behaved like this and never had latency this high number before. Can anyone give some hints?