Hi
If you have not yet done so, then it may help to update your iPhone and Apple Watch to the latest compatible software versions, starting with your iPhone:
- Update the iOS on your iPhone, iPad, or iPod touch - Apple Support
- Update your Apple Watch - Apple Support
Also check your Breathe reminder settings:
On your iPhone, in the Watch app, go to: My Watch (tab) > Breathe > Breathe Reminders.
Note that, under watchOS 4.x, Apple advises that scheduled Breathe reminder alerts will not be provided when:
- A reminder coincides with an event in your calendar.
- You are moving.
- You are exercising.
You should instead receive the reminder a short time after your event is over or after you stop moving.
Apple also advises that, if you start a session manually, then your Apple Watch will reschedule your next scheduled reminder.
More information:
Use the Breathe app - Apple Support
If you remain concerned that Breathe reminders are not being delivered as expected, then I suggest that you contact Apple Support or make a Genius Bar reservation for assistance: