When you add a file to the chest you are only making a copy of the file in the chest, you still have to deal with the original. There is no need to this as this is the expected behaviour, if avast detects a file as infected then it moves it to the chest removing the original.
Presumably you are adding a file to the chest because avast doesn't consider it infected but you do ?
If so confirm the file is infected:
heck the offending/suspect file at:
VirusTotal - Multi engine on-line virus scanner and
report the findings here, post the URL in the Address bar of the VT results page.
If multiple scanners detect it - Send the sample to avast:
Send the sample/s to avast as a Undetected Malware:
Open the chest and right click in the Chest and select Add, navigate to where you have the sample and add it to the chest (see image). Once in the chest, right click on the file and select 'Submit to virus lab...' complete the form and submit, the file will be uploaded during the next update.
Note: manually adding to the chest doesn't remove them from the original location, so they still have to be dealt with in that location. Presumably this is the way you manually quarantined it ?
Or
Send the sample to
virus (at) avast (dot) com zipped and password protected with the password in email body, a link to this topic might help and undetected malware in the subject.