Persistent Heart Rate Monitoring Issue on Apple Watch Ultra 2 & 3

For the past year, I have been reporting a recurring issue related to heart rate monitoring on my Apple Watch Ultra 2, and now the same problem is occurring on the Ultra 3. Despite multiple iOS updates and the replacement of the Ultra, the issue persists.

The malfunction occurs exclusively during outdoor workouts (typically walking or running). With both devices, the issue generally begins approximately three weeks after the watches were purchased, then escalates to weekly occurrences, and then becomes almost every two days.

The only temporary workaround is to turn it off and on. Notably, ECG and other heart rate measurements function correctly outside of workouts. However, when the heart rate is not detected during a workout, the watch fails to display distance and calories.

Additionally, since the latest iOS 26 update, notifications during workouts are no longer functioning, despite being enabled.