I have encountered this issue on the Enduro a few times. It is not clear to me what is causing the issue. I am able to get this working again, normally by Restarting my Phone. A couple of times I restarted both the Phone and the Enduro.The indication I have that there is a problem is I am still receiving Notifications on my older Garmin 920XT. The other item or issue I can note is the Activity I completed using the Enduro fails the sync to my Strava account.
I never see this problem on the Older Garmin Forerunner 920XT.