You could try splitting the SSIDs on your router and testing the connection between the 5gh channel and the 2gh channel, some phones operate better with just 1 channel selected.
Log into the router (192.168.1.1 etc ) and manually change the SSID (Wi Fi) name of the 5ghz channel.
I often find it is better to keep the 2 broadcast channels separate. For example, I have changed mine, and call one Home2Ghz and the other Home5Ghz. Some devices can drop the connection when the SSID's remain the same.
Also, you can try manually setting the wifi channel for each broadcast channel. Try channel 6 for the 2ghz channel and 44 for the 5ghz channel.
Give this a try , test with both SSID's and see if the connection improves.