It probably could--but it's still in beta and there are a lot of acceptable translations that the course doesn't yet recognize
It could. You should report it. As jsmitten said, the course is still in beta.
What's the indicator showing that an adjective you agree with the noun class or not? I thought this might be "mazingira masalama." I know if that it was "mazuri" it would agree. Why is salama different?
I think because it is of Arabic origine, and adjectives that come from Arabic or English are usually unchangeable.