Go to your phones WiFi settings and tap on forget your WiFi router then reconnect using your router's password. This is a bit like turning your PC off then on when it's misbehaving.
I hope this helps.
No doubt others will come up with other suggestions if you are still having problems.
I'd also try rebooting your router by unplugging its power for 30 seconds. See this guide for other ideas: http://forums.androidcentral.com/am...roubleshooting-wi-fi-connection-problems.html
Have you tested your phone on somebody else's router to see if it's the phone or the router causing the problem? I'm using a Moto G5 running 8.1 with no problems.
There is a possibility that the phone and router are not compatible. I had a similar problem 2 years ago with a Samsung tablet, replaced the router, problem cured.
If possible, I'd strongly advise uninstalling 360 Security. They're in the same league as Cheetah Mobile in terms of questionable app behavior.
I might agree but worked fine till 8.1 update..is the incompatible now there..could be but not replacing the router it is Comcast's and all there stuff runs off that..cable,phone and inet.