Err you’ve called the users endpoint and refer to something in the streams endpoint?
What are you displaying the thumbnail in?
Currently I’m seeing a thumbnail of the format
https://static-cdn.jtvnw.net/previews-ttv/live_user_STREAMER-{width}x{height}.jpg
So it never changes.
So depends what you are doing if this data depends on whats next, based on your post, I had no advice on what to do to fix the issue you are reporting