This morning I was Avast emergency update progress running on Task Manager while starting my PC, and after that I’ve had two avastui.exes running side by side constantly.
Repair Avast:
Control Panel> Program and Features (Add/remove program)>Select Avast> Select Repair. Reboot when completed
https://www.avast.com/faq.php?article=AVKB204
If Repair doesn’t fix the problem, try the following:
Clean Install of Avast:
https://goo.gl/4Ptzkf
That seems to have fixed the issue, thanks 
It was rather weird though, since when I rebooted my computer, my PC spent some minutes viewing “Preparing Windows” screen that shows up after system upgrade, and after that I was sent to a desktop with default Windows 10 wallpaper and desktop program icons (and my own folders were nowhere to be seen), with a notifiction “Microsoft failed to sign in to your account”, telling that if I did not try to log in again, I could “loose unsafed changes and files”. I tried out the re-login option it offered and I managed to get back into my normal PC account normally. Is that normal? :-\
EDIT: at least it didn’t seem to happen again after another reboot I did as a test
You’re welcome. 