I tried signing up and scanning apkmirror.com but it immediately came up with a 403. Perhaps your user agent is blocked, you should probably use a custom user agent.
It is cloudflare that blocked us, we scrape using a regular chrome instance (with the latest user-agent), but cloudflare are sometimes very aggressive in their blocking.
I'm busy adding a proxy option to handle these cases automatically, and some way to whitelist our scraper.