Apple Watch: Long run data and activity sync issues

A developer of an Apple Watch running app analyzed the issue and found out that Apple is doing unnecessary heavy processing on custom (interval) workouts:

"When you store structured workouts, it saves workout with multiple activities.

When finishing workout, HealthKit does a huge processing to associate all HKSamples to each activity, and it's a very huge amount of data.

It takes longer than before and can crash on slow/low battery watches.

It has always been super slow, but it's even slower now ..."

This explains why doing more intervals more likely causes the workout to never save as the watch is busy processing the workout indicated by still leaving the Workout app open.

Please report a bug here: Feedback - Watch - Apple

There more users report the bug, the more likely Apple will notice.

I have finally found my people! Unfortunately we don’t have a solution. I too use custom workouts for run/walk and the longer the workout is, the less likely they are to ever transfer to the phone as an activity. (Original Ultra, iPhone 16 pro) Today I ran a half marathon and it never came over. It recognizes my rings progress through the end of the race, but nothing since, no stand hours, nothing.

What would be nice and would probably prevent this is if they specifically had a simpler run/walk alert timer that didn’t actually divide the workout into intervals. I don’t need 100+ tiny segments recorded, it’s just the only way to make my watch vibrate when it’s time to switch. When I do use an actual interval speed workout, it has far fewer segments than my run/walk long runs.

I have the same issue. It happened a month ago when I ran 15 miles. It happened today when I ran 20 miles. Never happens when I run under 6. I use custom workouts and was using a 7 min run, 1 min walk. In both cases, I exceeded the number of intervals I had set. I am wondering if that is the issue? I have set my total number of intervals to the maximum of 98 repeats to see if that solves it. I’m using an ultra 2.

Thanks! Please report a bug here so we have a slight chance that Apple gets aware of the issue and fixes it: Feedback - Watch - Apple

I am seeing exact same issue since last few weeks where each time I ran for more then an hour (anything over 6 miles), Watch Ultra 3 is exhibiting this issue. Workouts are either taking much longer time to show up (or sometimes never show-up on the phone (and even on the watch's fitness app) and in the fitness app. Interestingly my shorter workouts (like less than an hour long) are showing up fine (and almost instantly right after I end the workout on the watch). I just think Apple watch is not able to handle a bigger data set (> 1 hr workout data. This is quite frustrating and it never happened to me on previous watch (Apple Watch Ultra 2). This is quite frustrating and unfortunately we have to go through this after buying such an expensive watch. I called Apple support but their diagnosis was not helpful.

Exactly the same issue. Custom workouts take several minutes to save. Sometimes they do not save at all.

Issue started with watchOS 26.1.