I was having issues in AWS with Lets Encrypt SSL so thought I would share the solution I came up with its simple actually but I couldn’t find it on a thread so please delete this if the solution has already been submitted.
Ubuntu 18.04 that has Apache installed with current SSL from Lets Encrypt
After installing Openvas 9 (Version 7.0.3)
Edit /etc/default/openvas-gsa
ALLOW_HEADER_HOST=example.com
SSL_PRIVATE_KEY=/etc/letsencrypt/archive/example.com/privkey1.pem
SSL_CERTIFICATE=/etc/letsencrypt/archive/example.com/cert1.pem
save and restart Openvas
systemctl restart openvas-scanner
systemctl restart openvas-gsa
systemctl restart openvas-manager