I played last night and got the Failed Save error for autosaves. I then manually saved and didn’t get an error and figured it was just an autosave issue. I went to load the game today and the map is fully black (like, full fog of war, but everywhere) and all people, buildings and resources are 0’ed out.
I’ve closed out and restarted and reloaded the save multiple times and get the same result.
I would upload the save file but it is too big, even compressed.
Any way to recover it?
When the save failed, was the error message that was generated?
Other than that though, unfortunately there is no way to recover a failed save as it, quite literally, failed. It is corrupted. You can load an earlier save for the same settlement and keep going from there.
I figured. That’s unfortunate. Is there anything I can do to avoid that? It was just a no-mod plains map with nothing fancy.
There was an error message but i didn’t think to screen shot it or write it down last night unfortunately.
Without knowing what caused the issue, I cannot say what you need to do to avoid it, haha. 
If it does ever happen again, please report the error so we can investigate the root cause.