I've had my Vivosmart replaced with a new one, and I got it connected, but on the dashboard, it won't show my daily steps. All other data seems to be there.
check if it is activated as your current activity monitor.
Go to the connect.garmin.com page on a pc, and click on the little cogwheel icon next to the vivosmart.
Select device settings.
At the top of the settings page it should state "activity monitor" with a check mark.
If it does not say activity monitor there you need to activate it as such.
The only way to do so that i know of is, to rightclick the vivo in garmin express (not connect) on your computer and then delete it from express and from connect (express will give you the option to do so).
Then add it again (while adding it you will probably be asked if you want to replace your current activity monitor (which might still be your old vivosmart) with the new one).
Doing so should not result in any loss of data (but no guarantees on that).
Tried both of your ways and it still won't work. I don't seem to be able to sync back and forth from my Vivosmart. It says it's synced and the current Vivosmart is selected, but if I change something in my setting in Garmin Connect, it won't go through to the device. Getting very frustrated as the old one worked fine.