I had this issue few days ago for this given configuration:
Dell laptop connected to an external VGA monitor.
I used it for 2 months in extended desktop without problems, often disconnecting the VGA to walk around then plug it back and it would just extend again (or worst case had to disable extended desktop then activate it again).
Few days ago I unplugged it again,and at the time to reconnect the external monitor, no way for me to extend the view on this monitor. The external monitor is detected (I can activate extended desktop but there will be no signal, and my CCC app will also detect the external monitor). I tried it with a mate laoptop and it works perfectly fine.
I had disable the extended mode, reboot many times, and try all I could in the CCC app or Windows screen settings preferences.
What am I missing ?
Thank you in advance.