What worked for me?
The only solution that worked for me was deleting the derived data folders of the hanging project, i.e the derived data folders in above directory: ~/Library/Developer/Xcode/DerivedData/. Hope it helps someone.
What didn't?
As mentioned at other places, deleting MyProject.xcodeproj/project.xcworkspace/xcuserdata/ or MyProject.xcodeproj/xcuserdata/ didn't work for me.
