@ davexnet
I would say that the difference in VT finding it is that they would have the scan settings set to scan for PUPs.
You have found one area to enable PUPs scanning, but that is for the on-demand scans (needs to be set for each scan type, see below), which personally I don't bother with. As most of the files scanned in an on-demand scan are either dormant or inert, then the point in checking is lessened. The avastUI > Settings > Active Protection > File System Shield is the on-access resident scanner and you can/should set that to check for PUPs if that is what you want.
If I remember the Web Shield is set to scan for PUPs, if not that is an other area, the Mail Shield also has a PUPs scanning option, this is off by default I believe.
Why it isn't being detected in the on-demand scan rather depends on which scan you have set it on. Each different on-demand scan Quick; Full System Scan; Custom scan, etc. has to be set to scan for PUPs. Is it possible that you have set it for only one scan but are running a different scan.