I recently upgraded to OpenWrt 19.07.2 r10947-65030d81f3 and I can't figure out why the 2.4 Ghz is so slow on all devices. My ISP connection is 100 Mbps and I am able to get pretty close to that on 5 Ghz and via Ethernet, but the 2.4 Ghz network speed is variable, always maxing out between 10 - 25 Mbps no matter how close I am to the router. Bitrate on the 2.4 Ghz radio shows up as above 90 Mbp/s while 5 Ghz radio shows up as 60 Mbp/s.
So why is the 2.4 Ghz network so slow? I don't recall this being such a big difference before upgrading the firmware.
Scanning and switching from Channel 1 to 11 and back (no change)
Switching from 20 MHz to 40 MHz and back (no change)
Switched from N to legacy mode (download speeds dropped from 10 Mbp/s to 2 Mbp/s)
Changed encryption mode from WPA2 PSK (CCMP) (I don't recall what mode I was using before the firmware update)
Changed transmission power (problem exists no matter how close I am to the router)
Tried moving clients over to 5 Ghz network (currently 9 clients connected via 2.4 and only 1 on the 5 Ghz. I thought maybe the load was using up bandwidth, but then why would switching to 5 Ghz still allow almost full speeds? The issue is some devices can't connect to 5 Ghz and it would be great to take advantage of the larger footprint of 2.4 Ghz).
Haven't changed any of the other settings under encryption or advanced tabs.
Details on my setup:
Hardware: TP-Link Archer C5 v1 (Qualcomm Atheros QCA9558 ver 1 rev 0)
OpenWrt 19.07.2 r10947-65030d81f3
Updated and with clean setup without reusing any previous configurations
Wifi Mode on both LAN radios: Access Point
Separate SSID for 2.4 Ghz and 5 Ghz networks
WMM Mode: On
SQM Qos is installed with download limit set to 0 and upload limit set to 4800 kbp/s (ISP caps at 5 Mbp/s and cloud backups were bringing the network down)