4.15 C++ Transition Guide

HI,
after updating from 4.14.3 to 4.15.1 I encountered several errors. After fixing all the ones mentioned in this thread I know get a lot of
unresolved external symbol errors. All the errors are for new components which I wrote in C++.
The same code is compiling fine with 4.14.3. Does this has anything to do with the new include system?
Anybody experiencing the same problem?
Cheers