Using Leap 15.2 here. I do not use NetworkManager, but it is installed, apparently by default, and I did not touch this. Thus I assume that the installation is what is installed by default. And it has NetworkManager-branding-upstream and it does not have NetworkManager-branding-openSUSE.
The comment of the upstream package says
This package provides the default upstream configuration for /etc/NetworkManager/NetworkManager.conf. Specifically, it is not configured for connection checking against http://conncheck.opensuse.org. For, the version with connection checking, install NetworkManager-branding-openSUSE.
Thus, apart from the fact that @Sauerland points to the fact that having the correct package is a basic solution to the problem, my question is: why does the OP here not have the upstream version which it seems to be the default?