Hi there,
Sorry you're having this problem, that sounds time consuming and frustrating! To help me investigate what's going on it would help me if you could go through the process you normally go through when you create a post, taking screenshots of each step so I can see what you're seeing. I would especially like to see the insert media page with settings and the edit post page after you insert the image.
Could you create a draft or private post to model what happens so I can see it?
Thanks for your help!