UFUNCTION of based class cannot be called from blueprint

I have a DerivedClass derived from a BaseClass. In the BaseClass I declared some UFUNCTIONs.
If I create a blueprint from my DerivedClass I cannot call any of the UFUNCTIONs declared in the BaseClass.

The functions are just setters and getters. For example one getter is

int GetLevel() const { return level; }

and the setter is

void SetLevel(int value)
  level = value;

Am I doing something wrong? Do I need to set up the classes in some specific way?

Everything correct at least from what you showing here. What exactly do you mean by can´t call the Functions? Are they not showing up if you rightclick inside the Graph and type the name of said Function? Or some other odd behaviour? Aside from that you should add a Category to your UFUNCTION meta. Need to see more of the sourcecode to look for a mistake.

If you need Hands on examples just simply lookup Character that is derived from Pawn that is derived from Actor on github in case you use binary launcher version.

My class is defined like this:
class AFirstPlayer : public ACharacter, public CharacterStatistics
{ … }

The functions are declared and defined in the CharacterStastistics class and I’m creating a Blueprint from the AFirstPlayer class.

The class CharacterStatistics has no UCLASS on top of itself. Is that a problem? Because during creation I select None as parent class.

First off Multiple inheritance for BPs is not supported. You can add Interface as much as you want.

No UCLASS no BP functionality.

If you dont want the Character Statistic defined inside your Character and be usuable on other Actors than use a Component instead (Composition instead of inheritance)

So your problem is most likely the multiple Inheritance + not a UCLASS.