Pmed u for alternative

Dear Sifus

Good day.

I subscribe to 300Mbps Maxis Broadband package in Dec 2020, and the speed (with Asus Ax88u) was able to achieve around (using Speedtest, connect to 'Subang') between 300-310Mbps for the first 2 weeks. But.... it suddenly dropped till 90+Mbps after that, even after I restart and reset router few rounds. Then, I complained to Maxis, who requested me to change revert back to their tplink router, and then they sent Maxpert to my house to investigate. The Maxpert came and reset the maxis owned Tplink router, right after that, the speed was around 230-250mbps with TPlink Router. After the Maxpert left, I switched back to Asus Ax88u router, reset it, and able to get 300mbps. But, 2 days later, the speed dropped (again!) to 95mbps despite few round of reset (on Asus router) and restart (both router and modem). Since then, I get around 90-95mbps.

Pls allow me to provide the brief system schematic as follow:
- Maxis Modem (aka BTU by Fiberhome HG6240A)
- Router is Asus RT-AX88u, firmware 3.0.0.4.386_41249 (replaced Maxis Tplink) that connects to Modem/BTU via Cat 5E ethernet cable, with QoS, IPv6 & DDNS (cloudfare) configured. (tested speed with and without these setting, outcome still same)
- Intranet (to different rooms/space) with Gigabit Switch via Cat5E ethernet cable.
- Mesh Node (Asus AX82u firmware  3.0.0.4.384_10177) at upper floor, with Ethernet backhaul via Cat5E cable, that connected directly from Ax88u (not thru Gigabit switch). (tested speed with and without MESh configuration, outcome speed same)
- Wifi 2.4GHz and 5Ghz are separated with different SSID.
- about 20+ nodes connected to the network (70% connected via 5Ghz) at anyone time.

The speed (both wireless and hardwire LAN, at both Ax88u and AX82u end) was around 300mbps before it drop to 90-100mbps. The speed testing was performed using speedtest.net, Nperf and fast.com from Dell XPS Laptop (with WIFI6 AX200 module), thru both WIFI6 (5Ghz) and Ethernet Cat5E cable connection. 1 thing I notice that, the WAN port connection speed (that connect from AX88u to BTU) is only 100Mbps now. Previously the WAN port speed was indicating 1Gbps when the wifi and LAN speed was (capped) around 300mbps during the first 2 weeks (after switched from unifi in mid dec 2020) speedtest checked.

Currently, with these set up (Asus Router and Asus Mesh), the speed is running around 90-94mbps now. And for the past 2 days, my users (including me) are experiencing lost- connection (both Ethernet and Wifi) intermittently (for few seconds) during MSteam & google class session, not mentioning 'video loading' slowly. FYI, I never experienced 'video loading problem' during my unifi-time (with 100mbps only, and the same AX88u set up).

What surprised me was that, when I switched back to Maxis-Tplink router (again & again), the speed is in the range of 250-270mbps without fail.

Would appreciate if Sifu could help me to resolve this issues for these Asus routers. Is there any special setting in Asus Router for Maxis Fiber? Or, is it possible that it is caused by BTU (from Fiberhome HG6240A) that incompatible wth Asus AX Router?

Thanks.