As I start experimenting with Xcode I realise that it is a tricky beast.
Xcode 10.2.1
I realised Xcode 10.2.1 used 100%+ CPU. I fixed that by reinstalling it completely.
Reainstalling Xcode I had managed to mess upp the simulators.
Error: Unable to boot device because it cannot be located on disk
Solution: Run in Terminal: xcrun simctl erase all
Xcode 7.3.1
Xcode 7.3.1 Fails to start on macOS 10.14.5.
0 Comments.