DIAGNOSIS The 2.4GHz band is congested or stuck in a legacy compatibility mode (like 802.11b/g). This crushes speed.
FIX Force the 2.4GHz band into modern, faster modes.
- Log in at router.asus.com, go to Wireless > General for the 2.4GHz network.
- Set Wireless Mode to N/AC/AX mixed or AX only.
- Go to the Professional tab for 2.4GHz.
- Set Bandwidth to 40 MHz and set Control Channel to 1, 6, or 11 (whichever is clearest in a Wi-Fi analyzer app).
IF THAT DIDN'T WORK A nearby USB 3.0 device (like an external hard drive connected to the router) can cause massive 2.4GHz interference. Move any USB 3.0 devices at least 3 feet away from the router or use a shielded cable.
HEADS UP The 2.4GHz band will never reach gigabit speeds due to physics. Expect a realistic max of 250-400 Mbps close to the router in ideal conditions. For top speed, always connect modern devices to the 5GHz network.