There are several reasons. It might be that the person removed you from their close friends list if they have one for story sharing. Or Instagram's algorithm might have messed up. Sometimes, if your account has had some violations, it could also affect what you can see.
It could be that you were unfollowed by that person or they blocked you from seeing their stories. Another possibility is a glitch in the Instagram app.
It could be that you aren't connected or following them closely enough. Sometimes, only close friends or mutual followers can view each other's stories. Also, there might be technical glitches in the app causing the issue.
It could be that your friend's account settings have changed, or there could be a glitch in the app. Sometimes, if your friend has a private account and has removed you from the allowed viewers list, you won't be able to see their story.
Maybe they blocked you or changed their privacy settings so you don't have access.
Maybe they've blocked you from seeing their stories. Another reason could be that your app needs an update. Sometimes, glitches in the app can also prevent you from seeing stories.
Maybe there's a glitch or a loading issue. Try refreshing the page or checking your internet connection.
Maybe your friend has set their story to private and only allowed specific people to view it.
Maybe it's a technical glitch. Sometimes Instagram has these random issues that get fixed after a while.
Maybe they don't have the permission or the feature to do it. Sometimes, your settings might prevent others from reposting.
Maybe it's a glitch in the app. Sometimes Instagram has technical issues that prevent this feature from working properly.
There could be a few reasons. It might be that the people who viewed your story have chosen to remain anonymous, or it could be a technical problem with the platform. You might want to try logging out and back in to see if that fixes it.