Here is what I have discovered.
Now and again, seemingly at random, while working in Storyline, I suddenly get jumped to another slide, and any changes I have made since working on that slide get lost. For example, say I'm editing a presentation and I've got up to slide 10 but I click in a box and the thing jumps back to slide 4. Then changes I've made since I last changed slide 4 seem to vanish, as if the whole presentation has been reverted.
Note: I am now working locally, not on a server, and the pathname and filename have no blank spaces etc in them.
Whether Storyline is generating executables or not is not relevant as far as I can see. And we're not doing that anyway -- all we're doing is writing slides at this point, just using tools within the Storyline GUI to insert perfectly ordinary features like quizzes, images, text and audio. We publish to HTML. Further, these are brand new presentations, not legacy products.
So what I have to do is this:
(1) Save after every single change, no matter how small.
(2) If it jumps around like that, exit the program _without_ saving my work, or the new version with all the changes lost will be written over the top of my last save.
To go back to my example, say I saved at the end of editing slide 9 then went to slide 10 and got jumped back to slide 4. If I save now, I'll lose all changes since I edited slide 4, but if I exit without saving I'll still have the new slide 9.