Ok so i did the same thing that BEEP did back on the 1/03/19.
Basically, went into my Virgin Superhub 3 settings using a web browser and typing in the IP address of the router, then signed in to the router back end. Once in, found the Wireless Signal settings and turned off 2.4Ghz and left 5Ghz on. I watched my phone automatically disconnect from the Wi-Fi and then reconnect itself.
The phone spent a whole half a day on the 5GHZ with no issues whatsoever. I only had to revert the router settings back to turning 2.4 on, because i discovered one device in my home, is still relying on 2.4 and cannot do 5Ghz. Sooooo.....again, Samsung what the hell is the fix for this? It would appear that the difference between a S8 and a S7 that both connect to a Virgin Superhub 3, is the S8 has no issues bouncing between the 2 ranges (if it even does this) and the S7 is falling over itself because it simply does not like 2.4Ghz. Sounds like a patch is needed to me?!!!