Why can't I tell Siri to "call mom" if her contact is listed as her name?

I have tried to tell Siri to "call mom" but it keeps saying "sorry, there was a problem with the app" and an option to open FaceTime. I have it listed under her contact that she's my mother, and it works on my iPhone and Apple Watch, but not on my Mac. so I thought maybe it didn't transfer to my Mac correctly, so I said "Susan Smith is my mother" and it said "ok but I already know that." can anyone help? thanks!