Major Bug in DNS Servers Text Field in System Prefs > Network > Advanced > DNS > DNS Servers

• Do you have a "Profiles" pane in System Preferences?

No, I can't see any Profiles pane.

• Is this machine part of a managed network?

No, just a 2012 Mini Mac I use at home, connected by Ethernet cable to a home router. This issue with the Network pane I only noticed recently (about a month or two ago I think). Nothing has changed on my home LAN network in that time, and previously I had no issues with the Network pane.

• Do you have any adware running?

Not that I am aware of, but just to check, I just downloaded the Malwarebytes to see if any adware is present, but there was none.

I have a HideMe VPN set up in my Network pane, but that has been there for a long time without causing issues.

• Do you know if this problem started happening around that time? Or did you just recently try to change your DNS?

Only very approximately about the same time. I had not looked at the Network pane for a while, but I happened to look at it about a month ago, and then noticed this issue. I installed ProtonVPN about 2 months ago I think. I also tried out the Hotspot Shield VPN not so long ago, and then later removed it from my computer. But this is well-known popular VPN that is a mature product and on the Apple App Store, so I presume it would not have such bugs in it.

• Are you running any other kind of security software? Or ad-blocking software? Or p**n-blocking software? Any of that could easily cause a problem like this.

No security software or antivirus software is running. I have the Ghostery ad blocker extension running on Safari. Turning this off does not help. Though I have not tried uninstalling it completely. I also have the uBlock Origin ad blocker add-on installed in Firefox, but this add-on is disabled.

Thanks very much for your reply. I've just tried it in safe mode, but the fault is still there. It is also there if I log in as root.

I also tried to delete the following Network pane preference files (I had to turn off System Integrity Protection to delete some of these):

com.apple.networkextension.uuidcache.plist

com.apple.networkextension.plist

com.apple.networkextension.necp.plist

com.apple.networkextension.cache.plist

But this did not fix the issue after rebooting.

By the way this is not the only Network pane bug I am experiencing: if I go to System Prefs > Network > Advanced > Hardware, and try to change the Configure option from "automatically" to "manually" in the pop-up menu, as soon as I select manually, it instantly reverts back to automatically.

And if I go to System Prefs > Network > Advanced > TCP/IP, and try to change the Configure IPv4 pop-up menu, again, if I select any menu option, it instantly reverts back to its original value. So I cannot change the Configure IPv4 settings.

If I go to System Prefs > Network > Location (the pop-up menu at the top of the pane), and using Edit Locations..., add another location, that new location also suffers from the same bugs described above.

In terms of unusual software on my Mac running in the background, there's very little. I run Carbon Copy Cloner, Dropbox, a text expander app called Typinator. Quitting Dropbox and Typinator does not fix the issue.

By the way, I am not sure if it is related, but on the Google Chrome browser on my Mac, pages sometimes fail to load the first time, and I get this message: "Your connection was interrupted. A network change was detected. ERR_NETWORK_CHANGED". This only happens in Chrome, not in Firefox or Safari.

The VPNs I normally use were set up manually by me, using the Network pane and standard Mac interface for VPNs. These have been running for years without causing any issues.

I did however some months ago try out a VPN called ProtonVPN, which used an installer and had its own app running. I have removed ProtonVPN and all the associated files I could find from my machine, but whether this might have made changes to my machine elsewhere, I am not sure.

Are there any Terminal command lines that can be used to reset all parameters connected to the network?

Because there are several tabs in my Network pane in which I am prohibited from changing the settings, it's almost as if some command has been issued which has frozen the Network pane and prevented me changing any network parameters.

Thanks very much for your help, etresoft.

I finally figured out the cause! I just unplugged my computer Ethernet cable from my router, and as soon as I did that, the Mac Network pane started working normally again! And when I plugged the cable back in, the Network pane issues reappeared.

My router is not a standard commercial one, but an OpenWrt router (alternative firmware). I was having some issues with bufferbloat on my regular Netgear computer (the Internet getting really slow when others are uploading), and since most commercial routers suffer from bufferbloat, the only option to fix bufferbloat was to buy a pre-flashed OpenWrt router, which is engineered to avoid bufferbloat.

Most of the settings on this OpenWrt router I do not understand, as it's pretty complicated. So I guess some months ago I must have made some changes to my OpenWrt router configuration that caused this problem. I know that one of the changes I made on my router some was to assign predefined LAN IP numbers to all the devices on my LAN (this was on the DHCP and DNS page of my router's configuration), so perhaps that caused my router to override the Network pane. I am going to revert those router changes, to see if that fixes the problem.

Thanks anyway for all your help and suggestions, it's much appreciated.

I don't think it is the VPN, as I removed the VPN configurations by removing one of the preference files, and this made no difference.