The first time Avast Full Scan didn't found malware. But after turning on PC, it auto-detected malware. False positive, Bug, Scareware or something else?

[NON]

Virustotal or full scan shows static detection only, but behavior shield detection (starting with “IDP:”) is dynamic (during-execution) as the name suggests.
This means, Virustotal does not show Behavior shield detection at all.
Also, these detections may be difficult to reproduce also because of behavioral basis.

Some logs may be placed below, depending on settings.

C:\ProgramData\Avast Software\Avast\report