I think this most often happens if you accidentally signed into the wrong “shard.” You would think smart things wouldn’t let you do this, but it does. You’ll be able to sign in but you won’t see any of your actual devices.
If that doesn’t work, look to see if your devices are listed under “my devices” but you are still missing the “my smart apps” tab.
If that’s true, then contact support, because something is definitely wrong.