GSA SER do not scrape and test public proxies anymore.
I was using GSA proxy scraper up to recently but, I had only a few proxies appearing and since it wasn't enough I added some more public proxies from the list.
I didn't change anything in my settings (apart from adding public proxy lists on top of my proxy scrapper's proxies)
and the soft do not check and scrape proxies anymore. I have to add them manually once or twice a day.
check the vid. http://screencast-o-matic.com/watch/cbjr6mlLkW