Datafield replaced with default field on vivoactive HR

I got feedback from vivoactive HR users for my datafield. They say that after installing the app settings can be set and it seems to work. But after starting the activity again the datafiel is replaced with a default field (timer).

I can't check this on a real device. Could someone test it on a vivoactive HR?
Is this happening also with other fields? Is this a known bug?

My datafield works fine in simulator. I uses it on a F3 without problems. Vivoactive has enough memory. The datafield only uses basic functions (current HR, current timer, app settings). I can't see a reason why the field gets deactivated and replaced by a default field. If the datafield would crash, then I would expect the IQ-logo and no replacement.

Here is the datafield:
https://apps.garmin.com/en-US/apps/4885b1e1-7102-4c66-8600-c69f911780d6

Thanks for your help.

Greetings
Ronny


Edit:
Other comments from users:
The datafield can be used with activity cycling but it don't work with running or workout.