This looks like an issue within the scanner, more specifically Community feed unusable + Are there any difference in using 1 Maximum concurrently executed NVTs per host in OpenVAS9 than the default of 4? i’m moving this thread into the “GSE” category.
Please make sure that you’re using the latest version of the GVM components listed in either GVM-10 (stable, initial release 2019-04-05) or GVM-9 (old stable, initial release 2017-03-07)