Whole scene gone! Missing Prefab (pink) after reloading a scene

My game is in a scene called MAIN.
I created a temporary scene for the sole purpose of making a 2D screenshot of an item that was to be an icon in the inventory. I created the icon.
In Unity I made a new folder, called Inventory icons,
In Finder I placed the icon.png
Back in Unity I was expecting a quick “importing thingy” message, there wasn’t one, but I didn’t think much about it.
I swap back to my MAIN scene to continue working, and EVERYTHING IS GONE, and apart from a pink plane, a directional light and a “Missing Prefab” Game object.

This exact thing has now happened twice.

What am I doing wrong?

Anyway to recover shit?

Mark

i’ve had this on an old overused laptop. gave me a few mental break downs, but on my newer laptop(by now a new pc) i haven’t had any problems, so it could be because of an old laptop/pc… if this is not the case then i have no idea what went wrong