Xayah Grades

I've been playing Xayah a good amount because she is very fun. I got mastery 5 with her but whenever I get an s with her it doesn't give a m6 Icon and I have not gotten a chest with her yet even though I have gotten many s grades on her. I went to my collection and It says my season highest grade with her is an A+ even though I have gotten many s grades. I just wanna know what I should do for this.