Thanks Grant for your response, I tried removing an cleaner application which I installed recently but it did not resolve the problem. I found solution through other threads from Tesserax as below:
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Network-related .plist files are created automatically if deleted. They are specific for your device and cannot be downloaded.
The ones used for Wi-Fi are:
- com.apple.airport.preferences.plist
- com.apple.network.eapolclient.configuration.plist
- com.apple.wifi.message-tracer.plist
- NetworkInterfaces.plist
- preferences.plist
To access them:
- Finder > Go > Go To Folder
- Enter: /Library/Preferences/SystemConfiguration/
- Click on Go.
I recommend that you move any that you find to your Mac's Desktop, and then, restart your Mac.