Make sure that you adhere to the limitations of the image sizes supported for the different live activities.
"_ ... for a Live Activity to use a resolution that’s smaller or equal to the size of the presentation for a device. If you use an image asset that’s larger than the size of the Live Activity presentation, the system might fail to start the Live Activity. ..._"
https://developer.apple.com/documentation/activitykit/displaying-live-data-with-live-activities