When in low memory, threads become almost sequential and many errors occur

### Expected behavior

this is my heap config : "${HEAP:="-Xms5g -Xmx5g -XX:MaxMetaspaceSize=1024m"}"
This memory and CPU look very normal
this is part of runtime log

### Actual behavior

I want to know why I behave strangely under high pressure and if it can be resolved

### Steps to reproduce the problem

there are my plugins

### JMeter Version

5.4.1

### Java Version

java version "1.8.0_144" Java(TM) SE Runtime Environment (build 1.8.0_144-b01) Java HotSpot(TM) 64-Bit Server VM (build 25.144-b01, mixed mode)

### OS Version

centos7