As the ISP gives you a 400 Mbit/s connection as you wrote in the OP, the modem/router they gave you should be capable to sustain that speed. The hEX is in a different position as you ask it not only to forward the traffic but also to do the bandwidth enforcement.
Also, you throttle the bandwidth to just 20/20 in total, not 20/20 per AP, so maybe this is the actual problem? What happens if you set the queue simple to 200M/200M?
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Hi Sir, I tried doing what you advised me to do to go step by step. I first restore my rb750gr3 to factory defaults and just configure basic WAN, LAN, DNS and NAT. Added fast track on DNS and no queue, bridge and pppoe configuration but the problem still persist. Server error on online games and web browsing are having problems just like before. At this moment, there are only 7 wireless routers connected to my rb750gr3 network and each wireless routers have 3-6 end users accessing the internet so there are, 21 - 42 end users devices connected and accessing the internet. Here is my config now.
# sep/20/2021 19:48:52 by RouterOS 6.46.8
# software id = 9SZJ-0LP4
#
# model = RB750Gr3
# serial number = CC220E7EFBE2
/interface ethernet
set [ find default-name=ether1 ] name=ether1-WAN
set [ find default-name=ether3 ] name=ether3-LAN
/interface wireless security-profiles
set [ find default=yes ] supplicant-identity=MikroTik
/ip address
add address=192.168.50.2/24 interface=ether1-WAN network=192.168.50.0
add address=192.168.100.1/24 interface=ether3-LAN network=192.168.100.0
/ip dhcp-client
add comment=defconf disabled=no
/ip dns
set servers=8.8.8.8,8.8.4.4
/ip firewall filter
add action=fasttrack-connection chain=forward comment="FASTTRACK DNS TCP" \
dst-port=53 protocol=tcp
add action=fasttrack-connection chain=forward comment="FASTTRACK DNS UDP" \
dst-port=53 protocol=udp
/ip firewall nat
add action=masquerade chain=srcnat out-interface=ether1-WAN src-address-list=\
""
/ip route
add distance=1 gateway=192.168.50.1
/system clock
set time-zone-name=Asia/Manila
Then I've tried to do some troubleshooting. I removed my computer's connection to the 16 port switch and connected it directly to the ISP modem router using 192.168.50.3 ip address. So now, my rb750gr3 and my computer are both connected to the ISP modem router using the same network with ip address 192.168.50.2 and 192.168.50.3. Tested the internet speed. Browsing and online games problem is still there. Web browsing still sometimes not responding and needed to refresh the browser for it to load while online games are getting server error connection. The ping reply to 8.8.8.8 is stable and no RTO.
Next I've tried to remove the rb750gr3 network connection. I removed the rj45 connection of the rb750gr3 from the ISP modem router so now it is just my computer that is connected directly to the ISP modem router. Tested the speed and everything is faster no problem encountered. Web browsing response was fast and loads automatically, online games doesn't experience server error connection and a lot times faster when logging in.
Why is it like that? is it because the modem router of ISP can't handle it?