I am playing a song and then I click on the three dots on my right.
Then I click on “Add to tags”.
I choose a tag, check the square, and quit from the window.
The song is correctly on that “tag”.
But, if I again, in the same song, click to “Add to tags”, that tag square is not checked, so I don’t know if the song is already inside that tag, the square is empty (but the song is correcly inside that tag group).
I tried to reproduce the behavior you’re seeing here, and things seemed to work okay for me. Can you share a screenshot of where you’re adding these tracks to tags?