No ideas on what is wrong, but make sure that your devices are NOT in local control mode. This will display for the HS100’s on the main page and can be reset in preferences.
I’ve been able to solve the issue just moments ago. I realized that one of the outlets was not sync loc/time, and this was the reason why smartthings app couldn’t identify it.
I need to go back to the Kasa app, click on sync (twice!!!) and only after that, all the outlets became visible in the smartthings app.