I have a similar issue. Alerts are not voiced in ANY workout types (so not only running).
What I realized is that the alerts don’t work if the watch is offline, but will work if the watch is connected with the Internet. My watch is Wi-Fi only and I don’t take my phone on my runs, so it’s always offline during workouts.
The issue happens even if the watch disconnects mid workout. It’ll start playing alerts and stop as soon as the watch loses connection.
Here is how I was able to reproduce the problem and my devices:
- iPhone 14 Pro on iOS 26, turned off to eliminate any connection to the watch
- AirPods Pro 2, connected to the watch
- Apple Watch 8 on watchOS 26
- Connected the watch to my home Wi-Fi
- Started a workout (could be any, I tested on walking and running)
- Manually ended a segment
- Alert played normally, saying segment duration
- Turned off the watch’s Wi-Fi, as there is no phone connected, the watch is completely disconnected to the Internet
- Manually ended a segment
- Alert stopped working
- If Wi-Fi is turned back on, it starts working again immediately
As I said, my watch doesn’t have cellular connection and taking my phone with me is not a viable workaround.
I tried changing the settings mentioned in this thread to no avail.