Adding local songs to my different playlists somehow doesn't work. Need help!

I recently added some local songs from my computer to my playlist and it worked out perfectly. But now that I wanted to spread them through my different playlists it just won't workout.

I can press the green dot with the tick in it and check the boxes for the playlists. Afterwards it also shows the message about the success of the process but then when I check in my playlists the songs won't show up. Also if I press on the green dot again the boxes on the different playlists aren't checked.

What can I do ?