Is it just me or does some of challenge questions not working?

Question

I was just challenging some people and there were questions like: what is the out put of this code;
Boolean b;
System.out.print(b);
And i firstly answered: null, but its said that i am wrong. After i checked the right answer after the battle and it showed that right answer was error, so i tryed to answer error next time when this question popped up and it still said that thats a wrong answer.
Same thing have happened with some other questions.
Soo is it just me and i am crazy or is it a thing?

Answer 1

Also question "Is a String primitive data type?" doesen't work for me. I have answered true and false, and both are not correct, but in answers it says that false is the correct answer.

Answer 2

Try to reinstall the app.

Answer 3

Ok, i'll try