Metabase says that scatter plots are incompatible with multiple series when trying to add another question, but if I first change both questions to show line plots, add one to another and change one or both back to scatter, everything is working well. Is inability to add to scatter plots a bug, or accepting them after first going through lines a bug?
Either way, it's hard to see why scatter plots would be any different in this context.
Many thanks
What version are you running?
v0.50.19
So I would say this is a feature request but you kind of find a workaround for it 
I guess 