I would like th have your help to diagnose very slow wifi speed, I tried a Roku devide and it couldn't keep up with 1080p and the diagnostic menu revealed high wifi glitch rate. I tested an old non-openwrt router and the Roku works flawlessly (same 2.4G band). I tested the bandwidth to be around 10.5mbps with iperf3 (server-client) and 80mbps with another old non-openwrt router.
I use this openwrt router as an AP specifically to separate different SSID into vlans (like IoT). the router is based on a Ramips MT7620 SOC (generic) and I use the image openwrt-19.07.8-ramips-mt7620-zbt-we826-16M-squashfs-sysupgrade.bin. 32MB FLASH 128MB RAM. Here's the link to the router if you are interested.
Could you tell me what would be the next steps to diagnose the issue? Thanks