Starting from the third level, nodes are shown with two asterisks less than expected. Trying to unfold them will actually fold the whole subtree instead.
The bug was present even with a clean Emacs configuration and nopackages installed. For the moment, I solved downgrading to org-20171023.
Thanks! Emacs : GNU Emacs 25.3.1 (x86_64-pc-linux-gnu, GTK+ Version 3.18.9) of 2017-11-02Package: Org mode version 9.1.3 (9.1.3-10-gadfbfd-elpa @ ~/.emacs.d/elpa/org-20171127/)