If you get another Avast alert, take a screenshot of it, also expand the window if it has an option for details/further information, etc and capture that info also.
As Far as logs go:
Assuming (dangerous I know) it is the file system shield, check the C:\ProgramData\AVAST Software\Avast\report\FileSystemShield.txt, but I doubt that that would give you any more detailed information than the alert. It could be that it is being initiated/recreated by another file/function (as in the C:\WINDOWS\Tasks\sysnetsf.job) that Sass Drake tried to remove in his fixlist.
It will certainly require further input from Sass Drake, when he is available. This may take a little while depending on your respective Time Zones and his available time (as a volunteer Malware removal specialist).
That's me for the night 1:30am here.