Using 2017 MBA with High Sierra. Randomly drops the internet connection. Sometimes several times per hour, sometimes once a week. Most of the time it also drops the WiFi connection. Have tried turning WiFi on and off, renewing DHCP lease, rebooting. All of these work or not on a random basis. I rule out the WiFi network itself since all my other devices maintain the signal with no problems (2017 iMac w/High Sierra, 2007 iMac w/ Sierra, 2006 MacBook w/OSX 8.6?, original iPad, and iPhone 8), even when situated at the same physical location. When the MBA drops the WiFi the toolbar icon at top drops out. But the Network panel in system preferences recognizes that the WiFi network exists and has a strong signal but is not joined. There are no other competing networks in my area. I also removed saved networks previously used when away from home. This random action does not seem to be correlated to sleep mode, long stretches of inactivity, keyboard actions, or anything else i can identify. Haven't yet found a cure in all the threads I've read so far.
It might be an incompatibility with your access point or issue with the driver. I had my driver crash several times, leaving the network stack unresponsive and requiring restart. This happened during a short power surge, leading to the router "almost" restarting (it's a Mikrotik router, the radio was down for a second, but not the whole router). Everything else reconnected (several iPhones, iPad and few other devices), but not my MacBook (at the time it was running 10.13 17A405)
Check your access point/router logs for a drop reason (if it provides any).
When this happens, you might do a wireless diagnostics report (option click on wifi icon, tap on ) and then search trough the files for some suspicious lines. After you collect several of them, open a bug report.
Another lead would be kernel based third party firewall solutions.