Hello Pyxi,
200 scenes is quite a lot I must say! There is no limit to the number of scenes or slides that can be added to a Storyline course, but a course will consume more computer resources the bigger it gets.
When making changes to your project, is the project file saved somewhere on your local directory, or are you working directly on a network drive? Working on a network drive has been known to cause issues with Storyline 360 project files, one of which is the inability to save changes.
If you are already working locally, try importing your project slides over to a new project file to see if this helps you save your file. If the issue persists, we'd like to take a look at your project file to investigate what's happening. Since your course might be too big to share here, please open a support case with our support team so you can share you file there.
Looking forward to hearing from you!