Not sure how we need up in a team room - I just created the room myself.Here is what helped, finally.I used the mobile version of Spark. It showed the missing button that I don't get from the web or Mac version of Spark and I could add more people. T...

It is not a 1-2-1 room. Screen shot below. The button to add people on the top right is absent in this room. It is there in other rooms, though...  

I am having the exact same issue .... This seems to be unrelated to the client used.