No way to see my last workout on Garmin connect. Sync seems to work, but workout is not appearing.
Do other past activities appear? If you could provide a screenshot, that would be helpful.
Have a look at - Troubleshooting guide for (some) data missing after syncing - Garmin Connect Web - Mobile Apps & Web - Garmin Forums
Since you say, "sync seems to work," I assume by that you mean the green circle is completed around your device icon?

I suspect item #4 is your issue, but it really could be a number of possibilities.