First of all, thank you for the interest in the topic.
You can see this more detailed post for the problem I encountered. The third-party library is mujoco (you can find the code here). mjCModel structure can be found in this folder in user_model.h file but the problem is encountered when I use AddGeom() where inside the code there is a new mjCGeom and this is the structure that cannot be initialized correctly. I have checked what you are saying and normally in construction the variables have some default values so not initialized variables is not the case.