I just logged in to my MacBook Pro (2015) running Catalina. While entering my password my desktop background disappeared, leaving a white background. On pressing enter, the machine suddenly rebooted. During the phase with the white loading bar and Apple logo on a black background the loading bar filled up (rather slowly) twice, and then showed an installation dialog:
The text says:
Installing on “Macintosh HD
27 minutes remaining
It didn’t say what was being installed. It didn’t remotely take 27 minutes.
After that it booted up again, with a very slow loading bar this time, slow enough for it to show a time estimate at around 8 minutes. I have to add that booting has always been lightning fast until today.
Just I logged in normally again, all my files still seem to be there, even my Safari tabs were restored.
I was hoping someone could tell me what happened (what was installed and why) and if there’s anything I should do or check now.