I seem to have the same strange thing happening, and I am also running Windows 7 (mine is 64 bit) with Avast and found:
Threat: RootKit: High Severity
Windows\inf\setupapi.ev1

I tried to apply an action when the scan finished, Avast asked to run a boot scan, it did so and found nothing but said my SAS processlist.db was corrupted, and did nothing to the infected file.

After reading what the OP did, I scanned the file individually with AVAST and Malwarebytes but it came out as clean.

I can’t find the scan.txt either, I do not have a /reports folder, hidden or not.