You might want to give the newly released Greenbone Community Edition 5.0.6 released a try (Now with GVM-10 instead of GVM-9 as used on GOS 4.3).
AFAIK there has been a lot of work done related on the feed update topic in this new major release. In addition the “About” menu is now showing which system operation currently is running so you should be able to see whats going on in more detail.