Has the upgrade broken reminders on Apple Watch?
I have iOS 13.1 on iPhone 8 plus and Watch OS 6 on an Apple 4. No reminders appear on my watch and I if I try to add one nothing happens.
Apple Watch
If you updated Reminders, then it will only play with other Reminders users that have also updated their Reminders app
https://support.apple.com/en-us/HT210220
Apparently there is a notice when you start Reminders in iOS 13 about compatibility.