I made some tests and i found something regarding to the problem, that Activities are not shown on the Forerunner 945, but just online in garmin connect or the app.
For me it seems the problem occures when the ativity has a longer pause in it. I tried it with commuting to work and badminton training. Normally for me going to and going back is "one activity", so i don´t save the activity when arriving and just press pause and shutdown my edge 520+. Afterwords i start it again and the activity and the ride goes on. If i do this, this activity does not show up on the watch in any way. If i record without these pauses the watch also shows them. Maybe someone can test this to verify this?