Subfinder 2.5.4 is intermittently returning email addresses instead of subdomains

[geeknik]

Describe the bug
Subfinder is intermittently returning email addresses instead of subdomains which hinders recon. There is nothing configured in my provider-config.yaml or my config.yaml.

Subfinder version
2.5.4

Complete command you used to reproduce this
echo "af.mil" | subfinder -all -r /opt/dns/resolvers.txt -o /opt/subs/us_air_force/subs.txt

(resolvers.txt is https://public-dns.info/nameserver/us.txt)

Screenshots

[vzamanillo]

It is the crtsh source. You can exclude the crtsh source as a temporary workaround.