I have a Samsung Galaxy S7 Edge. My router is an ASUS RT-N66U.
When I connect my S7 Edge to my 2.4 GHz Wi-Fi SSID, it never drops the connection. However, if I connect it to my 5 GHz Wi-Fi SSID, it drops the connection all the time, seemingly randomly.
I tried the suggestions online, like turning off IPv6 in my router (it was never on), turning off Bluetooth on the phone, turning off the Bluetooth scanning in the location settings, and other stuff.
What actually fixed it for me was changing my router’s 5 GHz channel. My router had auto-selected 5 GHz channel 161. This is quite near the top of the band, and with the knowledge that band-edge performance is sometimes compromised to pass compliance testing, I moved it down to channel 44. Since then it has never dropped the 5 GHz Wi-Fi connection. Whether this is related to band-edge performance on my S7 Edge, or the router, or whether it is not related to band-edge performance at all, has yet to be proven. Still though, it works.
I hope this helps someone somewhere!