I have recently purchased a used MacBook Air 13" from mid 2013 (Originally purchased October 2013). I know there have been a few owners before me. So it has seen some reinstalls in its lifetime. When the Mac has been in sleep for a while, and you wake it up, it does not automatically connect to a nearby wifi. Sometimes it detects no Wifi networks, other times it does detect the wifi networks around, but does not connect to any known ones. Some times if it has been on the charger over night, it might have a wifi connection in the morning. (I suspect Power Nap might have something to do with that) To solve it, all I do is to turn off the wifi antenna wait 2-3 seconds, and turn it back on. It then connects almost immediately in most cases. (Literally it goes straight to having a connection, and to the right network) Upon purchase I did a full reinstall of it with an AutoDMG image. The Mac is running macOS High Sierra 10.13.3 To permanently solve the problem, I have tried moving my home network to the top of the Wi-fi list, I have done a second reinstall of the Mac, with a newly created AutoDMG image. The SMC and NVRAM/PRAM have been reset, but none of it have helped. If you have got a trick up your sleeve, I am open to suggestions I don't think it had the problem with macOS Sierra, but I didn't have time, before the purchase to do a full test of it. I also don't suspect the AutoDMG image deployment to be at fault, since I use this on a lot of identical Macs, and none have exhibited this behaviour.