Well since these coming updates the share button has been kind of… broke… for lack of a better term…
The only way i know of sharing a song is
File → Save as… →
find a place to save your song and type in “.note” after the file name then click save
Go to songs here on the website and click the corresponding category your song is in and there should be an “Add song” button
click that and then select the “.note” file you just saved
To post links just copypaste the link from the url bar at the top on your song’s page
Does that help at all or would a few screenshots help?