[5.4.3f1-Mac] Entire scene wiped out after "failed to unpersist"

Hi,

To fix the background audio problem on Android, I updated to 5.4.3f1 last week. It did fix the bug as advertised but otherwise, that version is plagued with multiple issues (greyed out menu items, drag and drop issues, etc). However I just ran into a very serious problem:
- I'm using multiple scenes
- I was editing one of them: UI
- the editor gave me a bunch of "failed to unpersist" errors, which is not the first time. Previously I reloaded the editor to keep going.
- Which I did and upon reloading the UI scene is empty. Nada. Zilch. Nothing in it.

It has been years since Unity lost me a scene like that. I can't reproduce, so I don't really have a bug report to submit...