MCD asks me to repair it by the orange button, i click and it loads to repair. Then, it almost finishes, and at this points, asks me for permission to use UnrealEngine, that I accept, but doesn't even finish. it just comes to its original state, meaning asking me to repair it. I can click infinitely, it won't change anything and do it again.
I had the same issue, and I kinda just figured out how to fix it, Its the same solution as when somebody get the white screen while its open. Go into the installation location of your copy of minecraft dungeons, and from there you go "/dungeons/dungeons/Dungeons/Binaries/Win64" then start Dungeons-Win64.exe