Have You added the user as import feed owner?
Try:
gvmd --modify-setting 78eceaec-3385-11ea-b237-28d24461215b --value USER_UUID
Replace USER_UUID with uuid. You can get user uuid with the command:
gvmd --get-users --verbose
After You have done that, try importing. It should work now.
Also be sure that ospd-openvas socket is either in /var/run/ospd/ospd.sock or if You have it in another location, have modified the path in gvmd.
This is done with:
gvmd --modify-scanner=SCANNER_UUID --scanner-host=/directory/to/ospd.sock
Replace SCANNER_UUID with UUID. You can get UUID of OpenVAS Default scanner with
gvmd --get-scanners
If it still doesn’t work, check if You have NVT-s synced.
To sync, run:
greenbone-nvt-sync
Just saying, that all of this is documented in github and in release notes. Read the manual 
Sorry for bad formatting.