The servers are heavy with traffic
If Instagram’s servers are heavy with traffic because many people are using the app, stories might take a long to upload.
The file is too big
If the picture or video you’re trying to upload to your stories is too big, it might take a long time to finish uploading.
Slow internet connection
Using a slow internet connection can elongate the process of uploading a story on Instagram.
Some networks restrict Instagram and other social media apps, which might cause some features not to work properly.
Application is out of date
Your application may need to be updated to function properly.
Due to using a shared internet connection
If you’re using a shared internet connection, there’s a great possibility that the story is taking a long to upload because many people are using the network. (See Why Instagram followers dropped suddenly?)
Due to connectivity problems
If your internet connection keeps cutting off, it might elongate the process of uploading a story.
Due to using 3G internet
Using the internet over a 3G network may slow down the uploading of a story.
It’s a universal problem
There was a recent incident in May where Instagram’s stories feature wasn’t functioning properly. In this case, the problem was universal. (See Why Facebook is better than Instagram?)
Video doesn’t meet Instagram’s specifications
If the video doesn’t meet Instagram’s specifications regarding size and format, it may not upload.
The application was closed during the upload
Uploading a story might get interrupted and slowed down if the app was closed during it.