I did two installations of the RC1 Server yesterday and both of the machines have the correct grouping (only a single 2019 group with 4 items). I'm wondering if there was something in the sequence of the earlier builds that was to blame.

The installations were done on Windows Server 2016, but I doubt that has any bearing.

Would it be possible for you to uninstall the RC1 Server, make sure there are no leftover start menu items, and then reinstall?