And now we have everything we need to determine what’s the problem in your code. You have a circular reference between House and HOUSING. In order to initialize HOUSING we need to initialize House, but to initialize House we need to have HOUSING initialized already.
Honestly, it seems pretty strange that we can create many different instances of House, but HOUSING keeps a very specific instance for itself. Why do you need this buildings property? Why do you need House class and HOUSING enum separately? Maybe you should use sealed classes instead of enums?