There is an issue with the firmware on some Garmin watch models – notably the Forerunner 245 and 945 – which prevents third party apps such as TrainAsONE from downloading workout data.
We recommend all Garmin users connect to the Garmin Training service from their TrainAsONE services page https://beta.trainasone.com/services which can push upcoming workouts to their Garmin Training calendar, and onto their watch.
More details on the issue:
The TrainAsONE widget can download the workout summary, but any attempt to download the FIT workout data which the watch needs for the run will just timeout.
It appears to have been introduced in Garmin firmware version 3.90.
Garmin are aware of the issue, which is tracked on their forum: https://forums.garmin.com/developer/connect-iq/i/bug-reports/forerunner-945-firmware-3-90-appears-to-have-broken-trainasone-widget and are actively working on a fix
Unfortunately we cannot fix or workaround the issue our end – we have adjusted the TrainAsONE Garmin widget to try to catch the timeout and show the workout summary, and a link to this page