Dont think you can mix licences in the same licence group. The groups have to be made up of the same licence type.
Create a second group for the VMware vRealize Suite 2018 Advanced for vRealize Operations.
You are correct sir!
If I create a License group with just VMware vRealize Suite 2018 Advanced for vRealize Operations licenses (or a group with just vROps Adv 7 licenses), I can attach multiple licenses to the group, and it will automatically spread them out over the hosts that the group's filter picks up.