I have been troubleshooting my RT-AC5300 for several weeks. The 5Ghz-1 band is manually set to use ch36@80Mhz and I get up to 750Mbit/sec transfer between my wired pc and my samsung s10+. I was having issues with my 5Ghz-2 band. I tried every channel @ 80Mhz using the stock ASUS firmware and the Merlin firmware and both do the same thing. The signal strength on any channel (149-163) @80Mhz drops out completely or is detected very weak. Clients can connect but struggle to get anything...
Upper 5Ghz channels unusable at 80Mhz bandwidth
Upper 5Ghz channels unusable at 80Mhz bandwidth