Haproxy Load Balancer problem tes concurrent user jmeter

Hi, i have some problem with haproxy. I was find solution for long time, but not solved.
My Haproxy is run well so far. But, when tes using jmeter that stuck on about 80% success, but other is error.

My topology :
USER -> FIREWALL -> HAPROXY 2.2.4 -> {WEB_BACKEND 1, WEB_BACKEND 2}, {OTHER_WEB_BACKEND 1, OTHER_WEB_BACKEND 2} => DATABASE
** My backend using openlitespeed (try nginx too) and using nfs for store session.*

Haproxy On VM 2cpu 2GB ram
Backend On VM @ 8cpu 8GB ram

For Haproxy version detail : https://pastebin.com/ZeEiArDw
For Haproxy configuration file : https://pastebin.com/G8i4PHMy
For Haproxy log file : https://pastebin.com/SmfgbS5q

Jmeter using user/thread 100 or 200 ramp-up period is 1, always cannot get OK all, but about 80% OK. When stuck at slow loading, test with access browser is still normal and fast. But sometime get slowly on normal traffic. For Network is local network access. The test is only access index with no process access database.

Can someone help me?