So I ran into an issue today when trying to set a reminder on my Pixel 3 XL. I simply tapped in the persistent search bar on my home screen, typed in a reminder to call someone, selected the day and time as usual...and waited. Nothing happened. Watch for yourself.
While I don't have enough information from other people trying to set a reminder with the Google Assistant, Richard, who follows me on Twitter, informed me he was experiencing the same thing.
Are you experiencing this issue? Let me know and I'll see if I can bring more awareness to it.