It seems like a not uncommon bug (~30 million hits on google) is for your insta account to get into a state where it no longer plays music added to stories, instead displaying an error "This song is currently unavailable" (even though it plays for literally everyone else and it used to play for you just fine)
STEPS Using the instagram app, open a story that has music added (ie not music from the recording itself) (could be your story or someone elses)
EXPECTED Music plays
ACTUAL "This song is currently unavailable" (even for stories with music you know for a fact was playing fine for you before, and you know for a fact the music is playing for literally everyone else)
MISC My hypothesis is that this happens because insta has somehow decided the account is in a region where the rights to most music isn't available
When you account gets into this state, basically all stories with music added will generate this error
You can still add music to a story when creating it, but you're only given a small library of lame international public domain (or whatever) songs
What's weird is you can still search for the song you want, find it under audio and create your story that way - once posted it will play for everyone except you (because you'll still be getting the "This song is currently unavailable" error when viewing it)
What's also weird is that if you open the same stories (yours of those of others) in insta in a browser on a laptop, the music does play
And the same songs will also play fine when added to Reels
Last but not least I can't explain why insta/fb/meta would get the region wrong - at least me I live in the US and I'm not using VPN or anything like that, just the regular Tmobile 5g and my home wifi in FL, my insta and fb account are associated with my US phone no, US credit cards etc etc
I've filed two support requests for my account (@eightiestokyo) but as mentioned I'm far from the only one affected by this, if anyone has any light at all to shed on it that would be amazing