I have a new mac mini 2018 running Mojave. I copied my applications folder using migration assistant from my 2009 mac pro running Sierra, so Xcode version is 9.2.
Xcode starts and creating and building a single view app template works for both macOS and iOS.
But creating a playground results in endless spinning the wheel. I just add a line that prints the template "Hello, Playground" string to the console, but nothing happens on playground execution, the string does not even appear in the REPL Preview.
I downloaded Xcode 9.4.2 from the developer page - same result. I deleted, downloaded and re-installed 9.2, the same result.
I also downloaded Xcode 10.2.1 - here the playground seems to work.
Please note, that the problem already occurred when 9.2 was the only installation.
Following the advice from this thread: https://forums.developer.apple.com/thread/78869
I deleted these files in my user library, to no effect.
So what else can I do aside from re-installing the OS and installing every app from scratch?
UPDATE: I re-installed Mojave from scratch and installed nothing but 3 different Xcode 9 builds (9.2, 9.3 and 9.4) - in none of them does a playground work at all.