. Open the preference pane and uncheck the box. You'll be prompted to delete the local iCloud keychain. Confirm. Also disable it on the other devices. Delete the unwanted preferred networks from all devices. Then follow one of the procedures described in this support article to set up iCloud Keychain.
I've tried that too.
I went as far as to sign out of all iCould on all devices, delete the network plist files on the Mac and reset network settings on all iDevices, then signed in again.
It appeared to work at first, but a day or two later the old hotspots reappeared on the mac list.
My two theories are:
Deleting preferred networks doesnt remove them from iCloud, and the next time you make a change on any device iCloud restores them on the list on the Mac.
Second idea is that there is another location on the Mac that stores the preferred networks, and it is overwriting my list.
I suspect its the first option. I have also noticed that stored passwords in the iCloud keychain reappear after being deleted, however I would have expected other users to notice this problem..
For the benefit of anyone who happens across this article, I may have found a solution.
It looks like the local keychain may be conflicting with the iCloud one. If this is the case though, no amount of editing/repairing the keychain resolved it for me.
To that end, I logged out of iCloud in settings, then logged into another profile (an Admin) and deleted my user account - retaining the Home folder in its current location (I navigated to the home folder and renamed it to remove 'deleted' from the end to facilitate the next step).
I then recreated my profile, and pointed it to the retained Home folder from my old profile. Note that the home folder and profile name must match.
When I logged in, everything was exactly as I had left it - I logged back into iCloud, and was up and running in minutes. All the caches and keychains from the old profile seem to have been deleted, but if you use iCloud keychain, it will all restore properly.
The whole process took about 10 minutes, and the network error has not come back in the last 5 days.
I have been battling the same problem. So far, the only solution I have found is to log all devices off iCloud Keychain and then rebuild them one by one without restoring backups.
I tried the method of creating a new user account, which worked for a few hours, and then the old preferred networks came back again. I think they came back when a different user logged on to the Mac. I don't think I can take deleting each user account in turn (we have five accounts per Mac), it will be easier to just wipe the machines and start again.
Does anyone else have any ideas as to how to delete preferred networks once and for all?
I have worked out what was causing the old wifi networks to reappear. I have user accounts for each member of the family (5 of us). What I had to do was turn off iCloud keychain for every user on every computer, delete wifi networks for every user on every computer, then reset everyone's iCloud keychain, and then turn iCloud key chain back on for every user... on every computer.
I have been running now for 3 months with no more old wifi networks reappearing. It would be nice if when you deleted a wifi network, it actually got deleted.