It's hard to say for sure. Sometimes it could be due to server maintenance or a mistake in the system. You might want to check with the support team of the platform to get a clear answer.
It could be that your story violated some terms of service or content guidelines, causing it to be marked as unavailable. Or, there might be an issue with the file format or upload process.
Maybe there's a technical glitch or a problem with the platform where your story is hosted.