@Clive_A I just figured out what caused it. it's called "Bufferbloat". unfortunately, TP Link did not have a solution for this problem. I solved it the bufferbloat using smart queue management by...

I hope when they release this feature it applies to EAPs not just routers. most of my users are wireless not wired.

the combined bandwidth usage doesn't even come close to 50% of the available bandwidth. I'd imagine the speed should only slow down if the bandwidth was used at 100% utilization.

is it possible that my omada controller is hindering my internet performance? I have an omada software controller installed in an old 7+ year old PC and it get CPU spike to 90-100% every few seconds....

is there a way to extract the detailed information of my clients of given SSID?. I want their mac address to make a mac group to make the client stick to their designated SSID.

both. SSID and Client mac. via mac group in group settings. I use iperf3 LAN speed benchmarking tool.