Since updating my iPhone 6, and an iPhone SE to iOS 11.4.1, I’ve seen many disconnections from my wireless network at home. I’m running a Virgin SuperHub 2. After checking the config on that device, as well as the WiFi extender, I figured it was time to call Virgin to see if they could look in to the issue. However, I held back because my iPad Pro running iOS 12 beta, and my MacBook Pro running Mojave beta were both working just fine.
I realised this evening that perhaps iOS was the issue. I updated my iPhone 6 to iOS 12 GM, and the iPhone SE to the same, and so far, there have been no disconnects from the network.
iOS 12 ships in a few days on September 17th, so if you’ve been having problems then it should correct itself in a few days if you update. Alternatively, you can register for a free developer account and download the latest beta which is very stable.