version 8 and version 11 both use the same version 7 file format. So both versions should be able to open the same hosted file.
But there are differences in the features and capabilities of Version 8. If you have added features that were newly added in version 9, 10 or 11, those features will not work for the Version 8 user. Thus, if there is a start up script that uses such a feature, your version 8 user may have trouble opening the file.
That's just a guess on my part. There are a number of other issues to explore, starting from the exact method that your users are using to open the hosted file. Hosted files should only be accessed via Open Remote.