After having seriously problems including having to press the button to get my notebook (win 8.1, 64 bit, avast free) because it would not shut down/go into hibernation or sleep mode + other issues like Avast failing to load when it should, generally acting sleepy, etc, I suspected one of the latest updates, esp. the huge optional one, 723MB(?).
This morning I went to the Windows updates page, located it & uninstalled it. fortunately, no further issues caused & I did not have any of some of the loss of data & other issues others seem to have had.
everything is working fine again.
I hope Avast informs users, for example in a pop-up alert Update, that the this major issue has been resolved, something all will know about & soon!
Regards