Can scan one host fine, but not 20

[cfi]

Thanks for clarifying this.

@sawozny

[sawozny@openvas ~]$ openvassd --version
OpenVAS Scanner 6.0.0

Unfortunately this outdated version of the scanner could contain bugs like e.g. the following which could be responsible for this seen behavior.

• An issue which caused a scan to hang for ever if there was no redis kb
  available has been addressed.
  → openvas-scanner/CHANGES at v6.0.1 · greenbone/openvas-scanner · GitHub

You could try to review your redis setup based on Hint: Redis setup / configuration for GSE/GVM/OpenVAS - Greenbone Community Edition - Greenbone Community Forum but an upgrade to a newer release is still hightly recommended.