Apple fitness competition not working with one person

I have been competing with my sister for over 220 times over the years. all of a sudden a few weeks ago it has stopped. when I send an invite I get an error message. she can send me one , but I never receive it. I can see al of her activity, but we can't compete anymore. We both have restarted our phones and watches. software updates on both too. I can compete with other people but not her.