Hey, i have the exact same issue today, i can’t open my main project anymore but i can open others projects… Did you found a solution?
I found a solution that worked for me, following these steps :
-Duplicate your whole project so you don’t modify your main project directly.
-Open the copy directory, open folder Content
-Move the assets you suspect to make your editor crash in another folder (move them to Desktop is fine, for me it was Widget, so i moved the widget.uasset to my desktop)
-Then try to open your project, if it don’t crash you can start to replace your assets one by one until this crash again, this way you can isolate the asset make your editor crash and replace it by an older version of the asset (if you have a save) or recreate it.
Hope this help 
But even the oldest backup map isn’t working
- Open Config/DefaultEngine.ini and empty value of “EditorStartupMap”
- Open your project
- One of your assets on map is corrupted, find it and rewrite it.
- Continue with your project…
- ???
- Profit
Thank you for that helpful tip! I can now open my project again, but it crashes whenever I hit play and sometimes when I compile, which makes it difficult to deduce what is causing the game to crash. I did manage to get an error that said that I was accessing an index of an array that didn’t exist, so let’s see where that leads.
Every file uasset is working but files unmap isn’t working
Do you have Skype or TeamViewer? I show you what is wrong
I have Discord.
Have you found any clear reason why this is happening?
It has happened twice to my project this week.
On the first time I found that it was caused by three UI’s. I removed and remade them, and the problem went away.
Today I restarted the editor and this issue came back. Luckily I had a just commited to my version control software and was able to roll back.