High Sierra System Preferences Network pane is non-responsive

After installing a new system update, the System Preferences Network pane is often very slow to respond, update, etc. I'm talking maybe an hour before anything happens or appears, although at times it works normally, sort of. When Network is non-responsive, it hangs up all System Preferences functions for several minutes. It also doesn't seem to persist my settings; e.g., if I check the box to require administrator authorization to turn Wi-Fi on, sometimes I find it changed anyways and the box unchecked—even though the pane is password-locked.

I have tried *everything* to fix this, up to and including completely erasing my Mac hard disk, and reinstalling High Sierra and restoring my personal files (from a Time Machine backup) and apps—several times—to no avail. (Needless to say, this is quite disruptive; it's as though I got a new computer and all the accounts set-up and other set-up one needs to go through with that.)

Is anyone else aware of this issue and is there a fix that works for it?