I had this problem for weeks now, and after removing and re-installing Avast, it still persists. Avast will scan and stop at 50% with no explanation or error messages.
This is an iMac 21.5 late 3013 running OSx Sierra
Another issue, which I wanted to address before posting this, was to generate a support package however, the route described in the posts here, seem to be working differently for me as you will see in the screenshots attached, and I am unable to generate this package when I click Help → Avast Technical Support → Generate support package but get a feedback windows instead, which leaves no file when completed.
Please shed some light in this anyone.
Thank You