This looks quite similar to:
A difference between scanning a single host and a network could originating from e.g.
- Overloaded scanner host / too little resources (e.g. CPU or RAM) assigned
- Insufficient redis configuration (e.g. too low max databases or clients configured, please see e.g. Hint: Redis setup / configuration for GSE/GVM/OpenVAS - Greenbone Community Edition - Greenbone Community Forum)