For GOS 4.2 and GOS 4.3 a new patch level is available:
https://www.greenbone.net/en/roadmap-lifecycle/
These two releases fix the same bug about pre-conditions for upgrading the GOS release.
Only very few setups should be affected. In case the system does not allow you to upgrade, please contact the Greenbone Support Team who have a simple trick for you at hand.
In total each of the patch levels covers 1 improvement.