Underfull \hbox (badness 10000) error on \chapter{chapter name

[Giovanni di Bari]

I'm getting the error Underfull \hbox (badness 10000) at any chapter name.
Not only those with a long chapter name, such as \chapter{Quantization in Curved Spacetime}, which gets split into two lines, but also with shorter names such as \chapter{Hawking Radiation}