Edit: After half day, my wife’s Mac started having the same problem. I have then applied the solution that I found in the Apple
Update Software Automatically
If you want to constantly enjoy new features of Mac OS software or have security concerns, then you can schedule automatic software updates by following these steps:
1. From the Apple menu, select System Preferences.
2. Under the System group, select the Software Update item.
3. Select the Check for updates option and choose the check interval – Daily, Weekly, or Monthly – from the drop-down list.
4. If you wish, select the Download important updates automatically checkbox. It means that your system will not only check but also download available updates. However, if you feel that your Mac is running slow, better disable this option until your Mac’s performance is optimized.
To view the list of the installed software, go to the Installed Updates tab. Here you can see the versions of the installed updates as well as the date when they were installed. You can open this list as a log file when troubleshooting.