10.13 High Sierra Wi-fi issue

I called Apple support but that did not resolve wifi issue most probably as we can see from the posts here, because it is a problem of Sierra (occurred here the first time) and High Sierra upgrade. It is interesting. It was reported, that upgrading old (before 2009, which can normally not be upgraded any more) Macs to Sierra using a patch, the wifi would not work any more. Something in the Sierra and especially High Sierra upgrade is touching important wifi issues. So I think calling Apple support only makes notice to Apple that the wifi issue until now was not resolved.

I'm following this topic for a few weeks now because I'm having the same problems with my new iMac 27" (2017).

The iMac shipped with Sierra, I couldn't restore from TimeMachine because the OS was newer so I upgraded the new iMac to High Sierra 10.13.1 and restored my files back. All went fine until a few days later after two times the iMac was put in sleep mode, the WiFi signal drops out, it gets disabled and gets enabled by the OS but without any errors. During that moment the iMac gets really slow like it's going to crash. After two times waking from sleep, the iMac gets unusable because of lowliness upon enabling wifi. Quick solution was just let the iMac shut down instead of sleep, but a few days later I noticed that it began to happen even when using the Mac where the wifi just disables itself (not just losing the wifi network signal). It began to get frustrating. After updating to 10.13.2 it got even worse, it got to a point that I just couldn't enable wifi anymore. It was just disabled, trying to enable it in network preferences did nothing. Thank god that I have a long lan cable in my house to have some internet connection... So I searched the inter webs and found this article and some troubleshooting guides including removing the wifi settings from /library/preferences/systemconfiguration, reset SMC, reset PRAM, ... nothing worked. Even ran hardware diagnostics (no issues), used another profile, reinstalling Mac OS High Sierra, ... . Even that didn't solve it. The WiFi gets even disabled and re-enabled when you boot in rescue disk and try to reinstall macOS over the internet causing the download to halt and new reboot is required.

As the iMac is in warranty I contacted AppleCare (Belgium) where they helped out the best they could like all the stuff I already did to get it solved. They advised me to get my Mac back to the store to take a look at it but I'm afraid when reading all these reports that the issue wouldn't be solved at all.

Miraculously when I was in contact with AppleCare my wifi got re-enabled again, but still I have to shut down my Mac instead of sleep to keep it working. One sleep and I can remove the files at /library/preferences/systemconfiguration and reboot to get it up and running again. This ain't a good solution unfortunately.

I sincerely hope a fix is out soon because it is a bit frustrating.

PS.: my router is new, and on my old Mac there where no issues running Mac OS High Sierra 10.13.1,

Edit: SSID not hidden, connected to 2.4Ghz network since 5Ghz is unusable

I can't reset cause that's blocked by the ISP, I can login to the router but all those settings are locked. On hardware reset the ISP gives it back the SSID name that is known with them and i'm not allowed to change the name and password.

2.4Ghz test:

Did iMac to sleep mode, waited few minutes, braught it back (wake) and logged in. CPU usage goes through the roof (kernel_task 100% in activity monitor, see usage graph below during that time and after it reconnects), you notice the slowness when moving the mouse gets bumpy. After a minute, the connected wifi drops out, iMac tries to reconnect and that takes a few minutes and then reconnects again. The CPU usage then comes to a more normal level (as the image clearly shows).

My MBP rarely has the issue where I need to use it, and it's worked every time.

The older MB that I have, it needs to be done anywhere from once a day to once every two weeks. Since I started just removing it from the network panel and rebooting, it lasts a lot longer than just removing from network and trying to rejoin.

The for sure key for my networks; home and out in the public free wifi's:

is to disassociate first...

on my MBP, I usually don't have to reboot...

but on my older MB, often I do or put it this way, if I want a stable connection the next log in, I'll reboot on the MB.

The other thing that helps me personally; is setting it to the strongest signal; airport prefs joinMode=Strongest

One more note; on some wifi networks, especially the ones giving mac's in general a problem;

when I reset the mac address (sometimes several times until I find the right combo) that too also helps with SOME specific locations.

Instead of using a manual guess, I use a random setting and if for some reason the first does not work, and it's been known to happen - the second or third usually gives me a good long term connection. On my even OLDER MB, the first several 02:ab: have to remain a constant, and on one of my other laptops an old MBP it prefers the first two digits to remain the same & an older mb that died did the same.

So in my experience for me, the age will determine if you need to go the mac address change or not. The removal and or disassociation, some with reboot others without, usually gives me a long term connection.