You could never cast 2 concentrate spells
I'm not talking about 2 concentration spells. Spirit Guardians is a concentration spell but Sanctuary isn't.
Being able to run around with spirit guardians while under sanctuary would be hilarious.
Well, I'm not saying you should be able to and the Spirit Guardians would stop working as soon as you hit (or miss) a target with the aoe range, for example, but even outside of combat you can't combine these two and there's no rule reason that I can detect why you shouldn't be able to. If they say, well, it's too powerful then so be it. But then they should clarify that in the spell descriptions because it's not clear now. And Particularly when you cast Sanctuary first and then cast Spirit Guardians, the Sanctuary spell should be replaced and not cause Spirit Guardians to fail. In my opinion of course.