I had the same problem but literally fixed it right this second! I had 88 songs in my shazam history and only 44 songs in my shazam playlist on spotify!
I simply opened shazam on my phone, disconnected spotify account, then reconnected (or just delete your my shazam tracks playlist on spotify)
I then opened my shazam histroy to display all tracks iv previously shazamed, i selected all of them and then hit the spotify button at the top of the screen and it automatically transfered all 88 titles into a new my shazam folder!
Unfortunately this is not the solution anymore for there is no spotify button in the shazam history. 😞
I disconnected from spotify in shazam, deleted the playlist in spotify and then reconnected in shazam: The My-Shazams-Playlist didn't appear until I shazamed a new song. And then only this one song is added to the playlist.
How do I get all my previously shazamed tracks added to spotify's shazams-playlist?