I'm experiencing the same or similar issues with my Galaxy J7 (J700T). I'm going to try turning OFF the Smart Network Switch and see if there's a problem with the assignment of the IP address by the router. Will post again if neither or both don't resolve the PITA WiFi problems.
I think I've fixed the issue (at least a workaround) using an S8 connecting to a Virgin Media Super hub 2.
Login to your router
Go into the advanced settings
Enable 5GHz First Guest wireless network.
Choose an SSID - seems it must be of the form VM123456-5G. Where 123456 can be any 6 digits you like.
Untick "enable SSID broadcast" and don't give the SSID to anyone else- ever.
Enter a nice long password
Now on the S8:
Settings, connections, wifi.
Enter the SSID as the network name
Try connecting. I've been reliably connected to my home wifi for 3 days with no issues. Fingers crossed it holds.
This "solution" is via trial and error and reading posts by others.
Weirdly. It seems that the primary 5GHz network drops in and out all the time. Then the S8 doesn't auto-reconnect or at least tries too quickly. Or another device is bricking the connection when it reconnects- maybe Alexa? A static IP did no good for me.
This issue is NOT SOLVED. It has simply changed after the last update (Sept. 2018).
The difference now is, there is no exclamation mark next to the wifi, and the wifi IS connected at some low level. I am a tech with 30 years experience, and I have been examining this issue for months now...
Of course I have tried all the solutions offered: Toggle Wifi, Reset Connections, Cache Wipe, Full-Wipe. Spent two hours on the phone with Verizon, and then Samsung in Korea! THE PROBLEM RETURNS. I have been carefully examing the condition of this issue via the app called: WiFi Monitor Pro. I believe it is very good and accurate. Excellent tool. What is interesting... when the phone denies wifi data to most all apps (such as Youtube, AccuWeather, Yi Home, etc.) this app still shows low grade Wifi activity. So, after the update, the S8+ stays connected to it's wifi at some LOW software level, but firewalls the apps from access to the wifi they need.
Everything looks fine when you look at the WiFi icon, but one check into any of the wifi intensive apps will tell you the true tale of the condition of your phone. In this state the phone will NOT switch over to 4G for app data, and as such, YOU WILL BE BLIND TO INCOMING GMAILs, TELEGRAM MESSAGES, etc. This is a serious issue.
So, the problem is most likely in a software issue, and probably a low to moderate level Android OS Wifi management issue. It might be solved with an additional dedicated wifi router added to your network for your phone's exclusive use - as I think the issue might be DHCP oriented (particularly if you are turning wifi devices on or off daily). Well, the dedicated new wifi router is my next test. 4 months of daily toggling the wifi on this new S8+.
This issue is not as bad as the exploding batteries, but SAMSUNG, PLEASE FIX THIS PROBLEM!!!
spot on, issue only appeared for me after sep 2018 update. infuriating after buying expensive mesh wifi kit, samsung fix the issue or provide roll back to previous firmware
update, october 1 security patch level and latest update still hasn't resolved the issue, still useless connection to orbi rbk50 wifi. tell tale sign is orbi app wont connect to router even it shows wifi connected. Samsung do you even care? seriously every other device works perfectly.
Still having the issue where when I enter my house the galaxy S8 sometimes only connects to 2.4ghz instead of 5ghz band then I notice when I do the ipv6 tests my ipv6 doesn't work on my phone but ipv6 is still enabled and working. I'm using same SSID name with my router.
I have the same problem (computer on wifi fine, phone drops inexplicably).
I also have one much more irritating problem... when I move from wifi to data zones, my internet stops working completely. The only way to solve this is to restart about 3 times. Sometimes even this doesn't work.
I've tried switching wifi on and off, data on and off, data saving off, battery saving off, none of these make a difference.
Subsequently find this phone a real pain.
I just recently got my s8 and was having wifi issues. What i did was i went into the advanced wifi settings and i turned on "turn on wifi automatically". It is now working for me. Possible fix.