Wifi drops intermittently on Macbook Air
You've done a good amount of troubleshooting and at this point, you can probably assume the Mac hardware is probably fine make two conclusions:


your home router being different than the service router
your other devices re-connecting or reacting to your wifi differently


When the internet breaks on your Mac - you'll want to run the wireless diagnostics tool to determine what part of the chain is broken between the Mac and the internet.

Also - log in to the router and see if it still sees the Mac as connected (if your router can do that).

Look for the following:


Is the radio connected between mac and router
Does the Mac have a proper DHCP address from the router
Can the Mac ping the router
Can the router ping the Mac (or another device on the network ping the Mac)


If all of those are up - it's not your network and just a configuration issue on the Mac.

You'll probably need about three times of data collection and then a follow on question for someone to assist with diagnosis.