"Failed to save, Interactive file is missing or invalid"

My issue is similar to the one in this thread, but there was no clear resolution to that. I am working on a number of storyline projects downloaded from a third-party website. I've been making small edits in Storyline, publishing for LMS, and then uploading them as zipped files to Go1, which is the platform we use to make SCORM content play in Teams. 

This worked fine for my first 5 or 6 projects, but since then, I have not been able to successfully upload any zip files. When I try, I get the error message "Failed to save, Interactive file is missing or invalid". When I try the same thing on SCORM Cloud, it says "Course import failed: zip file contained no courses".

When I compare the problem zip files with the ones that worked, I can see they have far fewer files contained in them. But my workflow has been exactly the same for all of them, so why would they be different?

I've attached two storyline files here, one called Success, which I managed to upload to Go1, and one called Fail, which did not work. I'd be grateful if anyone could have a look for me and point me in the right direction.

Thanks