Something weird is happening with Avast Free 2014.9.0.2018: it does not start a weekly scan. It does not matter if it is a standard or custom scan, if it is programmed to start at sunday (it does not matter if it at morning, noon or afternoon).
And, ¿from monday to saturday? Yes, it work perfectly. So, ¿it is was made it to take sunday as a day-off? So, ¿why not programme the scan in another day? Because the sunday is my day-off. Period.
If so you need to have the option to wake up the computer to run the scan. If a laptop, etc. if it is on batteries there is an option not to run the scan.
AvastUI > Scan - Select the scan you are going to run > Settings - Scheduling.
This isn’t by design, it should work on all days scheduled.
That said - With a resident on-access antivirus like avast, the need for frequent on-demand scans is much depreciated. For the most part the on-demand scan is going to be scanning files that would be otherwise be dormant or inert. If they were active files then the on-access file system shield would be scanning them before being created, modified, opened or executed.
I have avast set to do a scheduled weekly Quick scan, set at a time and day that I know the computer will be on. If for some reason my system wasn’t on, no big deal I will catch up on the next scheduled scan.
NOTE: my scheduled weekly scan is set for just 00:15 am on Sunday and that works just fine on both my XP Pro and win7 systems and both of those often start from standby.
Unfortunately I don’t use win8.1 so I can’t test that, but it would be strange if this were only on win8.1 and this is the first instance I have seen on this never on Sunday issue with scheduled scan.