If you haven't already done so, avast needs samples:
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.
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 false positive/undetected malware in the subject.
A link to the site that is also the host in the submission report might also help, so that it to can be analysed and hopefully added to the network shield malicious sites list.