Same problem! Just had an iphone 6 and it worked fine, upgraded my phone last week to an iphone 8 plus and I am unable to do it share songs from Spotify to Instagram Stories. I've uninstalled and reinstalled both apps, logged out and back into both apps and nothing has worked. Continually asks me to log into Instagram and when I do just brings me to the home page with no option to share.
spotify version 8.4.75
Instagram version 67.0
phone is brand new & updated - this thread won't let me incude specifics but i'm as up to date as possible.