I have the same problem. I can select the tags in Admin form, however, when I press Save, the selection disappears.
I spent the last week with searching what the problem could be, no solution found yet...
When I enter the tags in legacy form, and save, the tags are saved. As soon as I open the Seblod Admin form, the tags from the legacy form disappear too.
Can you please explain to a dummie how to setup the fields and how to save the tags?