Just had my new Garmin Vivomove watch arrive, and tried it out by walking around the room, then syncing. It worked and wrote the steps to Apple Health.
Then I hopped on my elliptical and wore it while maxing the step counter. Hopped off, synced, then openned Apple Health... no new steps. Huh... :-\
Waited 10 minutes. Still no new steps. Quit Apple Health and relaunched, quit Garmin Connect and relaunched, tried disabling and re-enabling permissions for GC in Apple Health... still nothing. I still only see the few dozen test steps from a few hours ago :-(
What gives? I've had no problems with other apps reading and writing to Apple Health today. I've encounted issues in the past, e.g. Withings Health Mate couldn't read steps from Apple Health (despite three other apps doing so just fine), which is why I bought a Garmin watch instead, as it happens! Ha. But my current apps and devices are all working okay... except now for Garmin Connect.