The old hard drive must have had a few bad bits…
An option I can think of to save some content, is open your latest broken map.
If you have an area you want to save, like a building, select all the pieces and copy.
Open notepad and paste it in. name and save the text file.
make a few different text files of your all favourite things.
Then open your latest good snapshot.
Select all the text, copy and paste it into your viewport.
This will put the object in your map.
Props with custom meshes or materials may need these reapplied.
I don’t know if landscapes would work
and if you try it with devices, make sure you select all connected devices…but not sure if it will break references with them anyway, might have to check all events and functions of them to see if they are still connected