I see others also have this issue. Special definitions download grinds away for ever and ever and never seems to finish. Avast was just updated so that wasn’t the issue on this occasion.
I think it actually does but on some systems does not report that the download is complete and the boot time scan is ready to commence upon reboot. In other words, it’s a reporting error, not a download problem.
I stumbled upon this as I got impatient with the process which I knew from previous experience on other systems should have already completed in the same amount of time on the same network with the same data transfer rates. So I closed the Avast GUI and reopened it. I was intending to restart the special definition download process but when I clicked on the button it said the task was complete and I needed to restart the system to begin the scan.